Hattori Hanzo Masanari built this Jodoshu temple to memorialize the eldest son of Tokugawa Ieyasu. Hanzo Masanari (the elder) died at 55 years of age in the first year of Keicho (1596), and his grave is on the right side of Sainenji Temple. Hanzo Masanari was also known as a famed spear thrower, and was also called “Hanzo of the spear”. The beloved spear of Hanzo Masanari is held in Sainenji Temple.