Sakuma Morimasa (佐久間 盛政, 1554-July 1, 1583) was the son of Sakuma Moritsugu, cousin of Sakuma Nobumori, important Oda vassal of Oda Nobuhide and Oda Nobunaga. He was born in what is now Shōwa-ku district in Nagoya (located in Aichi district of Owari province).
He is an obliged of Shibata Katsuie and one of his best generals in several of his campaigns. Morimasa received from Oda Nobunaga the ancient fortress Oyama Gobo of the ikko sect located in the present Kaga prefecture.
The fortress was then named Oyama castle in 1580 and then Kanazawa castle. After several campaigns in which he participated, he received the nickname of "Oni Genba" which literally means "Demon Genba", Genba being his middle name.
After Akechi Mitsuhide's betrayal which led to the death of Oda Nobunaga and his heir Oda Nobutada during the Honnō-ji incident, Morimasa sided with Shibata Katsuie to make Oda Nobutaka (Nobunaga's third son) the heir of the Oda clan while Hashiba Hideyoshi (later Toyotomi Hideyoshi) supported Sanboshi.
Sanboshi is the heir of Oda Nobutada and still a child at that time. This dispute leads to the splitting of the Oda clan's retainers into two main factions led by Shibata Katsuie and Hashiba Hideyoshi.
The armies of both factions came to war. In 1583, Morimasa led an offensive against Takayama Ukon in Iwasakiyama.
Morimasa broke Shibata Katsuie's orders and defeated Nakagawa Kiyohide at the battle of Shizugatake in 1583, still ignoring Shibata Katsuie's orders, which led to his defeat as did Toyotomi Hideyoshi's forces which arrived the next morning.
Morimasa continually ignored orders to withdraw and did not abandon his post where he was engaged with the enemy. Despite his calls for reinforcements, he was finally defeated. Morimasa then attempts to escape but is captured and beheaded.
Morimasa's charge was the spark needed to start the battle of Shizugatake where Hideyoshi's troops were able to suppress any resistance led by Maeda Toshiie and prevented the support of Sassa Narimasa and Takigawa Kazumasu. In all, Hideyoshi's troops amounted to 120,000 men while Shibata Katsuie's troops numbered only 25,000.
This imbalance of forces finally forced Shibata Katsuie to commit seppuku with his wife, lady Oichi (younger sister of Nobunaga), following the betrayal of Maeda Toshiie.