Lifespan: Entoku 2 (1490) to 10/22 of Eishō 14 (1517)
Clan: Aki-Kumagai (descended from the Kunika branch of the Kanmu-Taira clan)
Lord: Ōuchi Yoshioki → Takeda Motoshige
Father: Kumagai Yoshinao
Wife: [Formal] Daughter of Miya Mitsunobu
Children: Nobunao, Nobutsugu, daughter (wife of Takeda Mitsukazu, wife of Misu Fusakiyo)
Kumagai Motonao served as a bushō during the early Sengoku period. A kokujin, or provincial landowner, in Aki Province, Motonao served as the head of the Kumagai clan. Motonao was the great-grandfather of an individual of the same name who was martyred as a Christian in the early Edo period.
Motonao was born as the son of Kumagai Yoshinao in Aki.
The Aki-Takeda clan descended from Kumagai Naozane, a bushō who supported the Minamoto clan in the Jishō-Juei War from 1180 to 1185. In the middle Kamakura period, his great-grandchild, Kumagai Naotoki, acquired landholdings in Aki. In the Muromachi period, the Kumagai served the Aki-Takeda clan, who at the time were district governors. This relationship between the Kumagai and the Takeda continued in the era of Motonao as well.
In 1504, Motonao, along with other kokujin from Aki, accompanied Ōuchi Yoshioki on a trip to the capital of Kyōto. In 1506, the Kumagai received territory from Takeda Motoshige. Before long, the Ōuchi family expanded their power in the Chūgoku Region and the Aki-Takeda came under their command.
In 1511, Motonao fought valorously at the Battle of Funaokayama. Thereafter, when the Aki-Takeda, with the support of the Amago clan, rebelled against the Ōuchi in a bid to restore their authority in Aki, Motonao sided with the Aki-Takeda.
In 1517, Motonao responded to a call from Takeda Motoshige of Imada Castle and joined in the assault of Arita Castle held by the Kikkawa clan who were aligned with the Ōuchi. Motonao served with the vanguard forces fighting against Mōri Motonari and Kikkawa Mototsune who arrived in support of the defenders, but was killed. Motonao was twenty-eight years old. He was succeeded by his eldest son, Kumagai Nobunao.
Distressed that the retainers could not bring back Motonao’s body from the battle, his wife traveled on her own to Arita to look for her husband’s remains. Although she located him, she could not bring him back on her own so she tearfully cut-off and brought back only his right arm. She washed the arm in the well at the family temple known as the Kannon Temple for burial in a grave.