Born into a branch of the powerful Fujiwara lineage, he grew up amid court prestige and provincial realities. The widening gap between Kyoto’s authority and local power in western Japan shaped his early ambitions.

As a youth he became familiar with sea lanes linking Harima, Sanuki, and Iyo, where shipping and tolls enriched local strongmen. These coastal networks later supplied ships, pilots, and intelligence beyond the court’s reach.

He cultivated influence among local officials and warrior bands who protected estates and moved taxable goods. Control over ports and storehouses let him reward followers, a crucial advantage in an era of weak provincial policing.

Reports of ship seizures and coastal attacks began to circulate, alarming estate managers and provincial governors. The raids targeted commerce around the Inland Sea, undermining the court’s fiscal base and public order.

He organized crews from fishing villages and armed retainers into a mobile force that could strike and vanish along complex channels. By combining aristocratic legitimacy with seafaring expertise, he turned banditry into coordinated rebellion.

Disputes with local governors intensified as he challenged levies and asserted control over strategic harbors. The confrontations signaled that his aims extended beyond loot toward coercing administrative power in the region.

Instead of sporadic piracy, his forces began hitting official outposts and transport routes supporting provincial rule. The campaign eroded confidence in Kyoto’s ability to protect subjects, emboldening local opportunists to cooperate.

He reportedly extended control inland by pressuring estate managers and recruiting disaffected fighters. The blend of intimidation and patronage created a proto-regional regime anchored by coastal mobility and local grievances.

As unrest spread in western Japan, the court classified his movement as rebellion rather than mere crime. crisis coincided with Taira no Masakado’s uprising in the east, exposing nationwide strains on Heian governance.

His forces struck Dazaifu, a vital hub for Kyushu administration and defense, shocking officials who relied on it to project authority. The assault demonstrated that sea power could reach deep into state infrastructure.

Kyoto dispatched commanders and mobilized provincial troops to crush the rebellion and restore maritime security. The operation reflected an urgent need to safeguard tax shipments, estate revenues, and the legitimacy of central rule.

Government commanders, including Tachibana no Tōyasu, coordinated local levies to counter his coastal strikes. The campaign forced Sumitomo to defend fixed positions, reducing the advantage his ships had provided in earlier raids.

As rewards and threats from officials intensified, some supporters reportedly shifted allegiance to save estates and families. Loss of ports and supplies weakened his ability to pay crews, a critical factor in sustaining maritime warfare.

Pursued by court forces and local militias, he was ultimately captured after his network of refuges narrowed. The defeat reasserted government control over key sea routes, at least temporarily, in western Japan.

He was executed following capture, and his death served as a public signal that rebellion would be met with decisive punishment. Chroniclers later remembered him as a symbol of maritime unrest and provincial autonomy in the Heian period.

After his fall, officials tightened oversight of ports and sea lanes, while storytellers emphasized the drama of coastal rebellion. His uprising became a case study in how local military entrepreneurs could challenge Kyoto’s distant authority.