The Japanese Pirates in the Warring States Period

 

Prologue: A New Perspective on Pirate History

Redefining "Pirates" in the Japanese Context

The cinematic portrayal of pirates—such as in Pirates of the Caribbean—often draws massive crowds, including families with young children. However, few viewers are likely aware of the fundamental differences between these onscreen swashbucklers and the historical seafaring groups of Japan, famously known as the Wokou (who operated from the 13th to the 16th centuries).

Unlike the massive Tall Ships seen in movies, Japanese pirates operated smaller, highly maneuverable vessels known as sekibune or hayafune (medium-sized raiding boats) and kohaya (small raiding boats). Furthermore, rather than being unlawful outlaws hunted, arrested, and executed by government fleets, Japanese pirates possessed a recognized, public character within their society. This legitimacy was defined by two primary roles:

1. Territorial and Fiscal Control: They controlled vital maritime checkpoints (fudaura) along seas, rivers, and lakes, where they rightfully levied taxes such as sekiyaku (toll fees) and uwanoriryo (on-board piloting/protection fees).

2. Naval Military Organization: They were highly skilled naval forces (suigun) that frequently integrated into the armies of feudal lords (daimyo).

While these maritime checkpoints were established by force during the medieval period, they were overtly sanctioned by contemporary society. Although sea travelers occasionally viewed these encounters as extortive when self-proclaimed seki or sekimori (checkpoint keepers) demanded fees on the open sea, the collection of these dues was considered a legitimate right.

These fees were categorized into distinct types:

• Hobetsusen: A sail tax imposed based on the size of the ship.

• Dabetsusen: A freight tax levied on transported goods.

• Uwanoriryo: An on-board fee paid to hire a pirate guide (uwanori). Having an uwanori on board guaranteed safe passage and protected the vessel from being attacked by rival pirate factions.

Historical evidence confirms the longevity of this system. In 1420 (the 27th year of the Ōei era), the Korean ambassador Song Hui-gyeong traveled to Japan to reciprocate an envoy sent by Shogun Ashikaga Yoshimochi. In his travel diary, Nosong-dang Ilbon Haengnok, he recorded:

"We hired Tozoku (pirates of the Eastern Seto Inland Sea) near Kamagari (modern-day Kure City, Hiroshima Prefecture) so as not to be attacked by Saizoku (pirates of the Western Seto Inland Sea)."

This passage demonstrates that the uwanori system was already well-established by the early 15th century. Over time, it evolved into an official maritime institutional framework utilized even by regional daimyo.

Consequently, the term "pirate" should not evoke images of lawless, hard-boiled mercenaries acting entirely on their own whim. On the contrary, they were respectable maritime warriors who rallied to the call of the Ashikaga Shogunate or local daimyo in exchange for fiefs or administrative positions (daikan).

Seeing the Forest for the Trees

Since the Meiji era, the historical study of Japanese pirates has accumulated a vast body of profound research. In recent decades, historians like Amino Yoshihiko argued the concept of "Sea-Faring People" (kaimin), while Katsumata Shizuo advanced the theory of "Samurai without a Lord." While these arguments garnered significant attention, subsequent research has leaned too heavily toward isolated micro-histories.

For instance, attempting to rigidly separate the "sea world" from the "land world" is largely unproductive. In the Seto Inland Sea, land and sea were inextricably linked; many prominent pirates simultaneously functioned as terrestrial magistrates. The sea served as a public highway, with the Seto Inland Sea acting as a vital artery binding the coastal regions of Chūgoku and Shikoku into a singular, interconnected socio-economic zone.

While active pirate networks existed elsewhere—such as in Kyushu, Kumano, Shima, and Chita—this study focuses specifically on the Seto Inland Sea. Controlling and organizing these specific pirate networks was of critical, strategic importance to national unifiers like Oda Nobunaga, Toyotomi Hideyoshi, and Tokugawa Ieyasu.

Because a vast portion of the Western Inland Sea fell within Iyo Province, influential pirate networks like the Murakami clan operated under the suzerainty of the Kōno clan, the hereditary military governors (shugo) of Iyo. The regional impact of this alliance is underscored in a document from the Mōri clan archives, where Mōri Motonari wrote:

"This time we send troops to Iyo in return, because Mōri Takamoto and all of us were saved by the Kurushima clan."

Motonari freely acknowledged that his landmark victory over the Sue clan at the Battle of Itsukushima in 1555 (the 24th year of the Tenbun era) was made possible by the naval support of the Kurushima clan—one of the primary vassals of the Kōno clan.

Similarly, in 1576 (the 4th year of the Tensho era), when Shogun Ashikaga Yoshiaki and the Mōri navy smashed Oda Nobunaga’s fleet at the first Battle of Kizugawaguchi to successfully resupply the Osaka Hongan-ji temple, the Shogun formally thanked Kōno Michinao for the Murakami clan's vital participation. This confirms that even deep into the Sengoku period, the Kōno clan was recognized as the peak of the maritime hierarchy.

Rather than merely studying these powerful pirate clans in isolation during their peak activity, it is far more critical to recognize that the Kōno clan, along with their distant relatives the Mōri clan (practically managed by Kobayakawa Takakage), operated as "pirate daimyo"—public authorities who ruled the waves at the close of the Warring States period. Unlike Eastern Japanese daimyo who relied primarily on land battles, these pirate daimyo secured and maintained their domains by exploiting maritime maneuverability and well-honed naval tactics. For example, Kōno Michinao successfully defended his domain against relentless invasions by Chōsokabe Motochika of Tosa entirely due to his clan's naval supremacy.

Consequently, any aspiring national unifier seeking to conquer Western Japan was forced to construct or co-opt a powerful navy. Kuki Yoshitaka, for instance, established himself as a premier naval commander under Oda Nobunaga by serving in the suppression of the Ise-Nagashima Ikko-ikki uprising (1574), the second Battle of Kizugawaguchi (1578), and the siege of Hanakuma Castle in Settsu (1580).

Under the subsequent Toyotomi regime, the traditional maritime structure underwent a radical shift. The Kōno clan was ruined, and the Murakami clan was forcibly relocated to Kyushu. Hideyoshi’s trusted daimyo—such as Tōdō Takatora, Katō Yoshiaki, and Wakisaka Yasuharu—occupied Iyo and Awaji, organizing local maritime populations into state navies deployed in the continental invasions of Korea.

At this historical juncture, the sheer financial power required to build massive battleships (atakebune) armed with cannons and matchlocks eclipsed the individual combat prowess of traditional pirates. The golden age of pirate lords—who tactically maneuvered sekibune and kohaya to incinerate enemy ships with hōroku-biya (earthenware-shelled explosives)—had come to an end. While some Murakami vassals left to serve Toyotomi loyalists directly, the Kuki clan maintained the regime's confidence due to their advanced engineering knowledge in constructing atakebune.

Some modern historians have overestimated Murakami Takeyoshi, labeling him a "daimyo of the sea" or a "unified maritime regime." While the Murakami clan enjoyed immense autonomy, they consciously operated as senior vassals to the Kōno clan and never aspired to bypass them to take direct orders from the Shogun or national unifiers. Past scholarship has failed to see the forest for the trees by focusing too narrowly on individual pirate groups, neglecting the broader power politics of the Chūgoku and Shikoku coastal regions shaped by these pirate daimyo.

The Survival and Legacy of Pirate Daimyo

This study pays close attention to the Kōno clan, particularly Kōno Michinao (?—1587), the final head of the lineage. Though a major pirate daimyo, the clan has long been overshadowed in mainstream history by the meteoric rise of the Mōri clan. Because several successive Kōno leaders were sickly or short-lived (Michinao himself died at 24) and plagued by internal succession disputes, local scholars have often dismissed them as a weak, minor power.

In reality, the Kōno were a distinguished medieval lineage rooted in Kōno, Kazahaya County, Iyo Province (modern-day Matsuyama City, Ehime Prefecture). Their ancestors included Kōno Michinobu, a key player in the Genpei War (and grandfather of Ippen Shōnin, founder of the Ji sect of Buddhism), and Kōno Michiari, celebrated for his bravery during the Mongol Invasions. In the Chūgoku and Shikoku regions, the Kōno were the only hereditary shugo family to successfully preserve their territory after the fall of the powerful Ōuchi clan of Suō Province.

The elite social status of the Kōno clan is evidenced by the high-ranking shogunal honors bestowed upon them. They were permitted the prestigious title of yakata—an honor reserved strictly for the Ashikaga branches, generation-long shugo houses, or those who rendered extraordinary service to the shogunate. They were members of the shoban-shu (the Shogun's elite entourage accompanying him to banquets and visits) and held the public office of Sakyo-no-daibu. Recent studies emphasize that the Muromachi Shogunate's honoring hierarchy was deeply meaningful to Sengoku daimyo to legitimize their authority; in this regard, the Kōno clan's social prestige vastly outstripped that of their rival, the Chōsokabe clan.

Furthermore, the Kōno bloodline held deep roots across Japan. In Mino Province (modern-day Gifu Prefecture), powerful figures like Inaba Yoshimichi (the famous Inaba Ittetsu, whose son Sadamichi became the first lord of the Usuki Domain), Hitotsuyanagi Naosue, and Hitotsuyanagi Naomori (first lord of the Saijō Domain in Iyo) traced their ancestry back to the Kōno family. Recent research has also illuminated a branch of the Kōno family (Yoshu-ke) that relocated to Kai Province (Yamanashi Prefecture), served the Takeda clan, and eventually became direct retainers (hatamoto) to the Tokugawa Shogun.

Recent excavations at the Kōno clan's headquarters, Yuzuki Castle, have shattered the traditional textual bias that painted the clan as weak. The site reveals a sophisticated, large-scale lowland hill castle surrounded by massive inner and outer moats and earthen ramparts. Excavated relics include vast quantities of premium imported Chinese ceramics, indicating a highly sophisticated, international lifestyle.

Moreover, the castle town of Dōgo was a bustling national hub for travelers and pilgrims, famous for its ancient hot springs and prominent religious sites closely tied to the Kōno clan. These included Ishite-ji (the 51st temple of the Shikoku 88-temple pilgrimage), Hōgon-ji (birthplace of Ippen Shōnin), and Isaniwa Shrine, one of the region's oldest sacred sites.

Toyotomi Hideyoshi first encountered this complex maritime society in 1577 (the 5th year of the Tensho era) during his campaign in Harima Province under Oda Nobunaga. From that point forward, Hideyoshi remained deeply entangled with the Inland Sea. His subsequent massive campaigns against the Saika of Kii, Shikoku, and Kyushu (1585–1587), followed by the continental invasions of Korea (1592–1598), forced him to continuously engage with the maritime populations.

Current educational and popular trends often view Hideyoshi's national unification as an inevitable, organic byproduct of regional integration driven by local daimyo, suggesting unification was achieved largely through diplomatic maneuvering rather than military force. I have long contested this passive view. Instead, I emphasize the agency of pirate daimyo like the Kōno and Mōri clans, examining how they made critical, existential decisions when confronting the unprecedented crisis of Hideyoshi’s expansion.

While these traditional maritime lords operated under the cultural and political values of the Muromachi framework, Hideyoshi championed a radical, transformative restructuring inherited from Nobunaga. This clash of fundamentally incompatible worldviews drove history forward. Hideyoshi’s unification systematically dismantled the hereditary, bloodline elites of the Muromachi era in favor of capable, technocratic bureaucrats—a process directly mirrored in his subjugation of the Seto Inland Sea.

To explore this dynamic, this study is structured around five core objectives:

1. To describe the multi-dimensional structure of the Seto Inland Sea pirate society.

2. To reveal how shrewdly Hideyoshi maneuvered and co-opted the vassals of these pirate daimyo during Nobunaga's final years.

3. To trace the transitional shift of maritime hegemony from the Kōno clan to the Mōri clan during the Sengoku-Azuchi Momoyama transition.

4. To analyze the relationship between the Toyotomi regime's successive "Pirate Prohibition Edicts" (Kaizoku Teishi Rei), the extinction of the Kōno clan, and the subsequent integration of the Murakami clans into the Mōri domain.

5. To evaluate the birth of the early modern Japanese state from a maritime perspective, focusing on Tokugawa Ieyasu's implementation of a comprehensive naval surveillance network.

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Chapter 1: The Historical Currents in the Seto Inland Sea

Land Battles and Naval Battles

How did Toyotomi Hideyoshi perceive a maritime society capable of altering the geopolitical balance of Western Japan? Born in Owari Province (modern-day Aichi Prefecture), Hideyoshi's early military experience was confined to the land-centric strategic landscapes of Eastern Japan. This background initially limited his capacity to effectively manage the unique naval dynamics of the West.

While warfare in Eastern Japan was fundamentally fought on land, naval capabilities were an absolute necessity in Western Japan. In the West, castles were strategically positioned along rivers, lakes, and coastlines. A warlord might successfully capture a fortification during the day, only to lose it to a devastating naval night attack launched by enemy pirates.

The integrated tactical reality of Western warfare is brilliantly detailed in the Buke Mandai Santō Kaizoku-ke Ikusa Nikki (The Military Diary of Generations of Pirate Families across Three Islands), compiled in 1663 (the 3rd year of the Kanbun era) by Mishina Heiemon, a vassal of the Kokura Domain. The text chronicles the Kawanouchi naval forces led by Kodama Narikata, a prominent naval commander under the Mōri clan during the Sengoku and Shoku-Hō (Oda-Toyotomi) periods. Among its entries is the Kawachi Keigo Oboegaki (Kawanouchi Memorandum of Naval Guarding), which outlines strict protocols for coordinated amphibious operations:

"When the Mōri army marches on land, the Kawanouchi naval forces shall sail parallel on the sea. The fleet of 250 vessels will be divided into five groups. Advancing in lockstep with the army's schedule, the fleet will sail 12 to 20 kilometers daily, maintaining constant contact. Because the navy can travel up to 60 kilometers a day while the army covers 20 kilometers, the fleet maintains a three-day operational buffer. To initiate contact, the land army will light a signal fire on a coastal hill, prompting the navy to dispatch a reconnaissance boat to exchange intelligence."

This highly sophisticated, simultaneous progression of land and naval forces was a unique hallmark of the Sengoku-period Seto Inland Sea. Neither Hideyoshi nor his lord Oda Nobunaga possessed a native naval organization comparable to these Western fleets. While Nobunaga eventually forced Kuki Yoshitaka—a pirate warlord of Shima Province—into submission, Hideyoshi lacked any inherent authority or personal naval apparatus to command the currents of the Seto Inland Sea. To expand westward, he had no choice but to individually subvert, negotiate with, and maneuver the local pirate networks.

Regional Divisions: East and West

Though modern observers often treat the Seto Inland Sea as a singular, uniform geographic region, it was politically and historically bifurcated into two distinct spheres during the Warring States period: the East Seto Inland Sea and the West Seto Inland Sea. The geopolitical boundary lay roughly between Bitchū Province in Chūgoku and Nii County in Iyo Province on Shikoku.

The East Seto Inland Sea was heavily oriented toward the political and economic orbit of the Kinai (Kyoto-Osaka) region. It was anchored by two of the most globally renowned Japanese ports of the era: Hyōgo (modern-day Kobe) in Settsu Province and Sakai in Izumi Province. The Hosokawa clan, who dominated the shogunate as Kanrei (deputies), maintained tight, lucrative relationships with these commercial hubs.

Vessels departing from these ports had to navigate narrow choke points like the Kitan or Akashi Straits, where powerful local pirate clans lay in wait. Around the Kitan Straits, the Manabe and Tannowa clans of Izumi, alongside the Kan clan of Awaji Island, held sway. The Akashi Strait was dominated by the Ishii clan of modern-day Akashi City.

Conversely, the West Seto Inland Sea was historically and culturally linked to northern and eastern Kyushu. Its primary commercial nodes included Onomichi in Bingo Province and the sacred island of Itsukushima in Aki Province. Standing as the critical nexus between the Eastern and Western halves of the sea was Tomo-no-ura (Tomo Inlet, in modern-day Fukuyama City, Hiroshima Prefecture). Located at the tip of a peninsula jutting into the Hiuchi-nada Sea, Tomo-no-ura was a naturally sheltered harbor flanked by hills and Taiga Island.

Tomo-no-ura owed its prosperity to a unique hydrological phenomenon: at rising tide, tidal currents flow eastward from the Bungo Channel into the Iyo-nada Sea, while simultaneously flowing westward from the Kitan Straits into the Harima-nada Sea. These opposing currents converge precisely at Tomo-no-ura. Consequently, ships traveling across Western Japan were forced to anchor here to wait for the turning of the tide, turning the port into an unmatched hub for national commerce and intelligence.

Due to this strategic prominence, Tomo-no-ura was deeply intertwined with the fate of the Muromachi Shogunate. At the dawn of the era, the founding shogun, Ashikaga Takauji, stopped at the port's Komatsu-dera temple while retreating from Kyushu to launch his counter-offensive on Kyoto. Later, his son Ashikaga Tadafuyu established his regional headquarters at Ogajima Castle here as the governor of Chūgoku. At the close of the era, the 10th shogun, Ashikaga Yoshitane, stopped at Tomo-no-ura while returning from exile in Yamaguchi to be reinstated under the military backing of Ōuchi Yoshioki.

Most famously, the 15th and final shogun, Ashikaga Yoshiaki, fled to this port after being exiled from Kyoto by Nobunaga. By appointing the Mōri clan as his deputy, Yoshiaki established the "Tomo Shogunate," turning this western port into the official high command for the anti-Nobunaga coalition.

The Maritime Lanes and Fortresses of the Murakami

During the latter half of the Sengoku period, the Murakami clan emerged as the dominant maritime force in the West, establishing their strongholds across the Geiyo Archipelago. The family was structured into three autonomous branches collectively known as the Santō Murakami (Three-Island Murakami) Navy: the Nojima, Kurushima, and Innoshima Murakami. While operating as nominal senior vassals to the Kōno clan of Iyo, they maintained a highly profitable alliance with the Mōri clan.

The Murakami expanded their hegemony deep into the Eastern waters, eventually assuming complete control over the Shiwaku Islands in Sanuki Province (modern-day Kagawa Prefecture)—including Hitsuishi-jima, Yō-shima, Hon-jima, Ushi-jima, Hiro-shima, Takami-shima, and Sanagi-shima. Situated in the Bisan Archipelago between the Harima-nada and Hiuchi-nada seas, the Shiwaku Islands were a vital maritime crossroad. The Shiwaku population provided elite mariners and pilots critical for transporting goods and travelers. By co-opting the Shiwaku mariners, the Murakami effectively institutionalized their control over the most perilous choke points in the Inland Sea.

Recognizing the threat of this expanding Murakami monopoly, Oda Nobunaga attempted to break their grip by issuing a decree through the Shiwaku Guardhouse on March 26, 1577, officially guaranteeing Shiwaku merchant vessels direct, unhindered shipping rights to Sakai. This document indicates that the Shiwaku Islands had become a highly contested ideological battleground; until roughly 1584, both the Murakami clan and the Oda-Toyotomi regime exerted overlapping, competing spheres of influence over these strategic waters.

Geographically, the Seto Inland Sea is an alternating sequence of open, turbulent seas (nada) and dense archipelagos: running from east to west through the Harima-nada, the Bisan Archipelago, the Hiuchi-nada, the Geiyo Archipelago, the Itsuki-nada, the Bōyo Archipelago, the Iyo-nada, and the Suō-nada. Between these nada lie narrow straits characterized by extreme tidal ranges and violent currents. Pirate clans fortified the islands embedded in these straits, transforming them into formidable "sea castles" (umi-jō).

For example, Nojima Castle—the primary stronghold of the head Nojima Murakami branch—directly commanded the Hanaguri, Kōjin, and Funaori straits. These narrow channels feature ferocious currents that top 10 knots (approximately 19 km/h), creating treacherous whirlpools. Similarly, the Kurushima Strait features a devastating 12-knot current at rising tide, generating the famous Hachiman-uzu (Hachiman Vortex). Ships navigating these waters were entirely dependent on local pilots; those attempting to bypass them were easily intercepted and captured from Kurushima Castle.

While the formal, structured "Seto Inland Sea Lane" is traditionally associated with the later Edo period, modern research proves that this comprehensive maritime highway system was fully operational well before the Sengoku era. It consisted of two coastal routes—the Aki route along the Sanyō coast and the Iyo route along the Shikoku coast—and three sophisticated offshore deep-water lanes that cut directly through the treacherous Hanaguri, Yuge, Funaori, Miyako, and Kurushima straits.

The Archaeology of Sea Castles

In recent years, our understanding of these maritime fortresses has expanded dramatically, driven by advancements in medieval battlefield archaeology and a wealth of fresh excavation data from the Geiyo Archipelago. This research highlights the unique structural layouts of sea castles, their international artifact profiles, and the fascinating presence of "reef pits" (iwashō-pittō) carved into coastal shorelines.

These reef pits are uniquely distributed across approximately twenty castle sites controlled exclusively by the Nojima and Kurushima Murakami clans. Archaeologists divide them into independent pits, column pits (carved perpendicular to the shoreline at fixed intervals), and rank pits (carved parallel to the shore in single or double rows). While independent and column pits are widely accepted to have held heavy wooden mooring posts for warships, the precise tactical function of the parallel rank pits remains a subject of ongoing debate.

Archaeological analysis reveals three defining characteristics of these sea castles:

1. Scale and Simplicity: Individual castles were remarkably compact, rarely exceeding the size of a standard terrestrial outpost. They lacked the elaborate earthen ramparts, dry moats, or extensive outer baileys typical of late-Sengoku mountain fortresses.

2. Amphibious Logistics: Because these tiny fortified islands lacked natural freshwater springs, their garrisons relied on secured water-supply stations positioned on the immediate opposite mainland shores.

3. Networked Geography: The fortresses were not positioned in isolation; their spatial distribution was deliberately planned to form an integrated defensive grid monitoring specific offshore shipping lanes.

A landmark excavation conducted by the Imabari City Board of Education at Nojima Castle—the historic headquarters of the Nojima Murakami—has profoundly altered our understanding of pirate life. The discovery, widely covered by the Asahi Shimbun and Ehime Shimbun in February 2011, unearthed extensive residential foundations and a fully functional blacksmith workshop.

Nojima today is a small, uninhabited island measuring roughly 850 meters in circumference, nestled in the rapid strait between Ōshima and Hakatajima. Directly south lies the smaller island of Taizakijima (260 meters in circumference). At low tide, the channel separating the two shrinks to a mere 20 meters. From the 14th to the 16th centuries, across the Nanboku-chō and Sengoku eras, these two islands were integrated into a singular, comprehensive naval fortress.

Excavators uncovered orderly, rectangular alignments of massive post-holes (40 to 50 cm in diameter) holding heavy architectural foundations within both the Southeast Keep and the Third Keep. Nearby, archaeologists uncovered a 1-meter-wide smithy complete with a haguchi (an unglazed clay tuyere/ventilation pipe used to connect forge bellows to a furnace), surrounded by thick deposits of vitrified slag, scale iron, and industrial forge debris. This confirms that high-grade iron weaponry was actively manufactured, repaired, and maintained directly inside the marine fortress.

Furthermore, the Third Keep yielded shattered fragments of massive Bizen ware storage jars capable of being reconstructed into vessels over a meter tall, alongside thousands of discarded, unglazed earthenware plates (kawara-ke) used in formal dining.

Hitherto, mainstream history dismissed Nojima Castle as a temporary, wartime emergency bunker, assuming the pirate elite lived permanently in comfortable mainland estates at Miyakubo on Ōshima. The discovery of permanent domestic infrastructure, industrial manufacturing, luxury imported Chinese trade ceramics, coins, and formal ritual dining vessels proves that Nojima was a fully independent, permanently occupied center of political and cultural authority. Here, the maritime elite conducted sophisticated samurai ceremonies identical to those held by the grandest terrestrial warlords.

Crucially, these major sea castles were almost always paired directly with fiscal infrastructure. Headquarters like Kaminoseki Castle in Suō, the Innoshima Murakami's Mikasaki Castle in Bingo, and the Nojima Murakami's Nii-Ōshima Castle in Iyo continued to operate as active, lucrative maritime tax checkpoints well after Hideyoshi issued his nationwide Pirate Prohibition Edicts in 1588. This strongly implies that the political authority of the pirate daimyo was structurally inseparable from their fiscal control over the waterways.

A Mobile Base: The Case of the Manabe Clan

The shifting fortunes and inherent nature of these maritime populations are perfectly epitomized by the Manabe clan of Izumi Province. Though later integrated into Nobunaga’s central navy, their ancestral roots trace directly back to Manabe Island (modern-day Kasaoka City, Okayama Prefecture) in the West Seto Inland Sea—illustrating the deep, fluid mobility that defined the seafaring families of medieval Japan.

The Manabe clan originally gained their distinct social status within the Seto Inland Sea as vassals of the Hosokawa clan, the hereditary military governors (shugo) of Bitchū Province during the Muromachi period. Over time, they expanded their territorial footprint into Izumi Province, as well as Nii and Uma counties in Iyo Province—regions where branch lines of the Hosokawa clan held significant estates.

Manabe Sadaharu (later known by his Buddhist name, Shinnyūsai) was the head of the clan during the Shoku-Hō (Oda-Toyotomi) era and founded the prominent Kii-Manabe lineage, which became one of the chief vassal families (karō) of the Wakayama (Kishū) Domain. Reflecting this prestigious status, Sadaharu’s life was recorded in the Meishin-Den (Biographies of Excellent Vassals), a component of the Nanki Tokugawa Shi (The History of the Nanki Tokugawa), a foundational compilation of the Wakayama Domain's historical sources.

According to The Thumbnail Biography of Lord Manabe Shinnyū, Sadaharu was recognized as a direct descendant of the legendary brothers Manabe Shirō and Gorō. In the celebrated epic The Tale of the Heike, these brothers were famous for shooting the rival Kahara brothers, Tarō and Jirō. The records further note that Sadaharu’s sixth-generation ancestor relocated the family’s primary seat from Manabe Island in the west to Tannowa in Izumi Province (modern-day Misaki Town, Osaka Prefecture). Today, the toponym Manabe-yama—associated with a moated circular tumulus—remains the sole physical vestige marking where the clan once anchored its regional power.

The historical accounts describe their fiscal operations explicitly:

"They established the Manabe Checkpoint in Senshū [Izumi Province], and all vessels sailing from Kyushu or Shikoku toward the Capital were required to pay sail taxes."

This indicates that the Manabe clan levied hobetsusen (sail taxes) at their Tannowa checkpoint on ships navigating past the Tosa coast of Shikoku or arriving from Kyushu as they attempted to enter the strategic Kitan Straits. In practical terms, the Manabe clan was exercising sovereign piratical control over the eastern gateway to the capital.

When the Hosokawa hegemony in Izumi collapsed, giving rise to the Miyoshi clan, the Manabe fluidly shifted their allegiance to the new regional rulers. In July 1547 (the 16th year of the Tenbun era), Sadaharu’s grandfather, Manabe Sadayuki, fought for the Miyoshi at the Battle of Shariji in Settsu Province, distinguishing himself by leading the vanguard charge ahead of 800 samurai into the enemy lines.

A monumental shift occurred in 1568 (the 11th year of the Eiroku era) when Oda Nobunaga marched into Kyoto. The samurai blocks of Izumi Province, including the prominent Matsuura clan who served as regional deputies, capitulated to his authority. As Nobunaga entered into his protracted, bitter conflict with the Ishiyama Hongan-ji temple, he recognized that choking off the temple’s logistics required a total naval blockade of Osaka Bay. To achieve this, he actively co-opted the maritime expertise of the Manabe clan.

According to the Biographies of Excellent Vassals, Sadaharu’s father, Manabe Sadatomo, was stationed at Ōtsu Castle in Izumi Province (modern-day Izumiōtsu City, Osaka Prefecture) to guard the strategic river mouths feeding into Osaka. In recognition of his critical role, Nobunaga granted Sadatomo extensive lands equivalent to half the holdings of a minor daimyo, fiscal stipends to maintain 1,000 men, and a massive monthly military supply of 600 kilograms of gunpowder.

This strategic deployment is corroborated by the Shinchō Kōki (The Chronicle of Lord Nobunaga), compiled by Ōta Gyūichi, one of Nobunaga’s personal archers and widely regarded as the most authoritative biography of the hegemon. In May 1576 (the 4th year of the Tenshō era), Sadatomo, alongside other Izumi-based samurai such as the Numa clan, was deployed to the vital coastal position of Sumiyoshi in Settsu Province to oversee maritime defense and contain the Hongan-ji forces.

A surviving shogunal decree issued by Nobunaga dated June 18 mandates Sadatomo and Numa Dennai to enforce strict patrols across Osaka Bay to sever the temple's maritime supply lines. Other contemporary family archives, such as the Hineno Documents, similarly verify Sadatomo’s execution of these aggressive naval blockades. Ultimately, this duty proved fatal; in July 1576, Sadatomo, alongside key members of the Numa clan, was killed in action during the catastrophic defeat at the first Battle of Kizugawaguchi.

The trajectory of the Manabe clan—moving their operational bases from Manabe Island in Bitchū, to Tannowa, and finally to Ōtsu in Izumi—captures the essence of the maritime warrior society. They executed high-stakes military blockades and enforced fiscal checkpoints under the direct mandates of prevailing land-based authorities, whether they were shugo, warlords, or national hegemons.

Crucially, their history highlights a fundamental sociological difference between maritime and terrestrial warriors: while land-bound samurai historically fought to the death to defend a specific, inherited plot of land (ichigo ichie), maritime clans utilized a flexible system of naval transfers. They viewed their bases as transportable assets, readily shifting their headquarters to adapt to changing political tides on the mainland. This high geographic mobility was mirrored by the dominant Murakami clan, who effortlessly managed multiple maritime strongholds across several provinces simultaneously without being anchored to a single piece of earth.

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Chapter 2: Technological Change and the Fall of Pirate Dominance

Naval Battles and the Proliferation of Firearms

The fact that Nobunaga provided the Manabe clan with 600 kilograms of gunpowder a month proves that maritime forces had already integrated a vast arsenal of matchlock firearms (tanegashima) into their tactical doctrines. This heavy expenditure offers vital insights into how the Oda navy was structured. In recent decades, the study of medieval Japanese weaponry has progressed significantly, shifting from a niche antiquarian interest into a vital framework for analyzing political and military history.

The historical introduction of firearms into Japan remains a subject of vibrant academic debate, characterized by three major schools of thought:

1. The Traditional Theory: The mainstream belief that firearms were introduced exclusively by Portuguese traders who drifted ashore on Tanegashima Island in 1543 (the 12th year of the Tenbun era).

2. The Wokou Smuggling Theory: Advanced by Udagawa Takehisa through extensive metallurgical analysis of surviving firearms and textual records. He argues that the Tanegashima event was merely an isolated incident, and that Wokou maritime networks had already been actively importing and using firearms acquired throughout Southeast Asia.

3. The Post-Wokou Network Theory: Offered by Murai Shōsuke through exhaustive archival research. He demonstrates that it was Wang Zhi—the infamous leader of the mid-16th century Post-Wokou, who operated vast Chinese smuggling rings—whose multinational junk brought the Portuguese traders and their Southeast Asian-adapted firearms to Tanegashima.

These sophisticated arguments collectively suggest that firearms entered Japan via a diverse array of maritime routes stretching from Ryukyu to the ports of the Sea of Japan, mediated entirely by seafaring smuggling networks.

Remarkably, archival evidence reveals that firearms were deployed in naval combat within the Seto Inland Sea a full quarter-century before Nobunaga’s legendary Battle of Nagashino (1575), where a massed volley of matchlocks famously shattered the Takeda cavalry. Bairin Shūryū, a learned monk of the Tōfuku-ji temple in Kyoto, recorded a vivid account of a maritime firefight in his diary on September 19, 1550 (the 19th year of the Tenbun era).

While sailing off Hibi in Bizen Province (modern-day Tamano City, Okayama Prefecture) around noon, Bairin's vessel was intercepted by a pirate warship. When frantic mid-sea negotiations collapsed, a fierce battle erupted. The pirates unleashed a volley of arrows, but Bairin's crew fought back using matchlock guns, inflicting heavy casualties and forcing the raiders to break off.

Because early matchlocks possessed an effective range of roughly 500 meters compared to the standard military bow range of approximately 380 meters, firearms offered an immediate tactical advantage on the open water. In naval warfare, where maximizing engagement distance was a matter of survival, Western Japanese warlords eagerly integrated firearms into their navies. A famous example includes the Ōtomo clan’s deployment of a massive European-style breech-loading cannon nicknamed Kuni Kuzushi (The State Destroyer). Decades later, during the Imjin War (the invasions of Korea), heavy firearms and shipboard cannons became the decisive instruments of naval combat, claiming the life of the celebrated Korean Admiral Yi Sun-shin at the Battle of Noryang in 1598.

The Tactical Evolution: From Explosives to Heavy Firepower

Two decades after the introduction of firearms, Nobunaga found himself locked in a desperate struggle for naval supremacy in the Seto Inland Sea against the Mōri clan and their maritime allies. In July 1576, the Oda navy suffered a crushing defeat at the first Battle of Kizugawaguchi at the hands of the combined Mōri, Kōno, and Murakami fleets. However, by the summer and autumn of 1578 (the 6th year of the Tenshō era), Nobunaga launched a revolutionary counter-offensive that completely reversed the naval balance of power.

The profound tactical transformation that occurred over those two years is laid bare when comparing two separate entries from the Shinchō Kōki:

The First Battle of Kizugawaguchi (July 1576):

"The enemy surrounded our fleet, blocking our passage, and rained down countless earthenware-shelled explosives [hōroku-biya] to incinerate our vessels. Heavily outnumbered and overwhelmed by fire, our lines collapsed, costing the lives of veteran commanders such as Manabe Sadatomo, Numa Iga, and Numa Dennai. The Western forces achieved a total victory, successfully shipping vast military provisions into the Ishiyama Hongan-ji temple before sailing triumphantly back to their western domains."

The Second Battle of Kizugawaguchi (June and November 1578):

"On June 26, in the 6th year of the Tenshō era, our newly constructed fleet sailed out from the Kumano coast toward Osaka. Off the coast of Tannowa, the enemy rowed numerous coastal boats out from Saika and Tannowa to swarm our massive vessels, launching a fierce multi-directional assault with arrows and matchlocks. Kuki Yoshitaka, commanding seven massive ships that stood as imposing as floating mountains, initially held his fire. Waiting deliberately until the enemy swarms pressed into close quarters, he ordered a sudden, coordinated salvo from his heavy shipboard cannons, instantly obliterating the leading enemy boats. Terrified by this overwhelming firepower, the remaining raiders could find no way to approach, allowing our fleet to sail unhindered into Sakai on July 17.

Subsequently, on November 6, a massive armada of over 600 warships from the western provinces advanced on the Kizugawaguchi estuary. Kuki Yoshitaka moved to intercept them. The enemy surrounded our fleet as we sailed southward, and a ferocious naval battle raged from eight in the morning until noon. Though initially hard-pressed, Kuki utilized the massive artillery mounted on his six primary vessels. Waiting until the enemy vessels closed in, he directed a concentrated cannon volley directly into the enemy’s flagship, sinking it instantly. Panic swept through the western fleet, and they broke off their assault. Kuki pursued them ruthlessly, driving hundreds of enemy boats back into Kidu Bay. All who witnessed the engagement praised Kuki Yoshitaka for his unparalleled military exploit."

The stark contrast between these two engagements illustrates a paradigm shift in naval warfare. In the 1576 encounter, the traditional tactics of the Seto Inland Sea reigned supreme: fast, agile, medium-and-small raiding craft (sekibune and kohaya) maneuvered to swarm slower vessels, isolating them before incinerating them with hōroku-biya. These hōroku-biya were round earthenware incendiary bombs packed with gunpowder, iron shrapnel, and lead balls—the dominant tactical weapon of the Sengoku maritime world. Over time, these evolved into sophisticated incendiary arrows, small rockets with stabilizing plumes, and primitive mortars fired from wooden cylinders designed to detonate upon striking an enemy hull.

The Izumi-based samurai under the Manabe clan, despite their bravery and strategic bases along Osaka Bay, lacked the tactical answer to these massed incendiary swarms. They were thoroughly defeated by the Murakami navy—the undisputed champions of traditional inland warfare—allowing the Hongan-ji temple to be resupplied.

In direct response to this disaster, Nobunaga bypassed traditional inland design, commanding Kuki Yoshitaka of Shima Province to construct a fleet of revolutionary, iron-plated "armored ships" (ōatakebune). These massive vessels were sailed from the Kumano-nada Sea into Osaka Bay. As detailed in the 1578 entries, these floating fortresses effortlessly withstood the matchlock fire and arrows of the Saika and Tannowa raiders, using heavy shipboard artillery to shatter the swarms.

In just two years, naval combat transformed from a game of close-quarters incendiary raiding into a duel of long-range heavy artillery. These ōatakebune were not merely reinforced to shield their crews; contemporary letters from the Society of Jesus (Jesuit missionaries) in Japan reported that these revolutionary vessels were armed with multiple large European cannons, effectively making them the world's first heavy ironclad battleships.

Years later, Kanō Mitsunobu—a master of the celebrated Kanō school of painting—captured this era of naval might in a detailed six-panel folding screen (byōbu) depicting Nagoya Castle in Hizen Province, the grand staging base for the continental invasions of Korea. His painting prominently features these armored ships, adorned with multi-storied wooden keeps (tenshu) built atop their decks. These floating keeps served as command towers for the samurai elite and functioned as potent visual symbols of the hegemon's absolute authority.

While equipped with auxiliary sails, these massive warships were primarily driven by rows of oars—ranging from 50 oars on medium variants to over 150 on the largest class, making them equivalent to vessels of 75 to 300 net tonnage. Heavily timbered, armored, and crenellated, these ships sacrificed speed for structural invulnerability and firepower. In battle, they operated much like modern naval formations: the ironclad ōatakebune acted as capital battleships, medium sekibune served as cruisers, and agile kohaya functioned as fleet destroyers providing screen protection.

Conclusion: The Triumph of Capital and State Power

This technological revolution signaled the end of the traditional pirate way of life. Naval warfare had fundamentally transitioned from a test of individual seamanship and tactical maneuverability to a contest of raw, industrial firepower and financial capacity. On land, the Azuchi-Momoyama era was defined by the rise of massive stone-walled castles topped with towering keeps; on the waves, this same architectural and military philosophy manifested as floating fortresses bristling with artillery.

While traditional maritime populations like the Murakami clan had spent generations accumulating highly specialized tactics as independent sea fighters, they completely lacked the immense capital reserves and timber resources required to construct, arm, and maintain fleets of heavy artillery-laden ironclads. This stark economic barrier explains the dramatic shift in maritime hegemony at the close of the century.

The independent, decentralized pirate lords of the Seto Inland Sea were rapidly marginalized, replaced by state-backed naval commanders operating under the direct authority and massive financial sponsorship of the central Toyotomi regime.