Yasumi Naomasa was a military commander in the Azuchi-Momoyama period

Azuchi-Momoyama period

The came at the end of the Warring States Period in Japan, when the political unification that preceded the establishment of the Tokugawa shogunate took place. It spans the years from approximately 1573 to 1603, during which time Oda Nobunaga and his successor, Toyotomi Hideyoshi, imposed order...

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A dominant retainer of Hatakeyama clan

Hatakeyama clan

The ' was a Japanese samurai clan. Originally a branch of the Taira clan and descended from Taira no Takamochi, they fell victim of political intrigue in 1205, when Hatakeyama Shigeyasu, first, and his father Shigetada later were killed in battle by Hōjō forces in Kamakura...

, he ruled Katano and Iimoriyama castles.
He conspired with Yusa Naganori and Yusa Nobunori to overthrow his lord. He then approached Oda Nobunaga

Oda Nobunaga

was the initiator of the unification of Japan under the shogunate in the late 16th century, which ruled Japan until the Meiji Restoration in 1868. He was also a major daimyo during the Sengoku period of Japanese history. His opus was continued, completed and finalized by his successors Toyotomi...

after falling out with Nobunori and served Nobunaga to guarantee his own safety.

Known as Yasumi Naomasa generally, one can verify only Yasumi Munehusa (安見 宗房) in papers.