Lifespan: 15xx to 15xx
Other Names: Shigeharu, Uemon (common)
Lord: Tokugawa Ieyasu
Clan: Nomi-Matsudaira (Achiwa family)
Father: Matsudaira Shigechika
Siblings: Gentetsu, Matsudaira Shigeyoshi
Children: Uemon (Gen’i), daughter (wife of Honda Tadakatsu)
Achiwa Gentetsu served as a bushō during the Sengoku period.
Gentetsu is surmised to have been a member of the Nomi-Matsudaira family.
Gentetsu is regarded as the eldest son of Matsudaira Shigechika, the second head of the Nomi-Matsudaira family, while Matsudaira Shigeyoshi, the third head of the family, was his younger brother. The Achiwa surname originated from their place of residence in the village of Achiwa in the Nukata District of Mikawa Province. The village of Achiwa was situated to the south of the village of Iwatsu. The family resided on the shores of the Aoki River, a tributary of the Yahagi River where the Atsuwa Shrine (a shrine listed in the Engi-Shiki) was established. Adjacent to the village of Achiwa in the Aoki River Basin were the village of Todo in which Aoyama Tadakado was a landowner and the village of Kuramae which was the birthplace of Honda Tadakatsu at Nishikuramae Castle.
In 1571, the forces of Takeda Shingen advanced into Mikawa and Tōtōmi provinces, and, in the third month, Asuke Castle fell. At this time, there was a movement among the residents of Asuke to ally with the Takeda and attack Okazaki. As a result, Tokugawa Ieyasu ordered Gentetsu and Tadakado to establish defenses to the north of Okazaki. In the village of Todo, Gentetsu and Tadakado installed fences, positioned soldiers, dispatched scouts, and, in the evening, built a fire in an iron basket and guarded the route to Okazaki. As anticipated, the ikki forces raided the village of Todo, but were not able to proceed further.
In the fourth month, villagers revolted in Tōtōmi Province and charged into Mikawa through the gateway of Tsukude, headed toward Okazaki, and set fires in the environs of the village of Iwatsu. Gentetsu, together with Tadakado and Aoyama Tadashige (siblings), in addition to Uno Kohei, rushed to the village of Iwatsu and defeated the enemy, after which they chased fleeing soldiers, re-engaging them at Mount Yokidogi. This is recorded as a violent clash during which numerous soldiers from the Aoyama family, including Tadashige, were killed in action. Meanwhile, Tadakado later died of injuries sustained fighting in the village of Achiwa (subject to other theories). The enemy forces withdrew from the gateway to Yoshida to Tōtōmi. Upon learning of the battle, Ieyasu later praised the valiant fighting of Gentetsu and members of the Aoyama family.
Thereafter, Gentetsu appeared to have died in a battle but the timing and location of the event are unknown.
According to one genealogy, Gentetsu had one son and one daughter. His son, Achiwa Uemon (Gen’i), served Honda Tadakatsu and, similar to his father, died in battle.
His daughter became the wife of Honda Tadakatsu and bore two sons and three daughters, namely, Komatsuhime (the wife of Sanada Nobuyuki), the wife of Okudaira Iemasa, Honda Tadamasa, Honda Tadatomo, and the wife of Honda Nobuyuki.
According to another source, Gentetsu only had one son while the wife of Honda Tadakatsu was Gentetsu’s granddaughter (Uemon’s daughter).