Masatoyo was the 2nd son of Kudo Toratoyo, who had fallen out with Takeda Nobutora (Takeda Shingen's father). The Kudo were banished from Kai and wandered from place to place in the Kanto, living for a while in a fishing village, before being called back into Takeda service by Takeda Shingen. The Kudo were restored to their old domain. Afterwards Masatoyo took over the Naito family and became one of Takeda Shingen's most reliable generals and fought in many of his battles (including the fourth battle of Kawanakajima (1561), the Battle of Minowa (1566), and the battle of Mimasetoge (1569)). He was given Minowa castle in 1566. Later, at Mikatagahara, he distinguished himself by leading a charge into the Tokugawa ranks. He was at the forefront of the fighting at the Nagashino (1575) and was shot many times by arrows before being beheaded by Asahina Yasukatsu. Oddly, the Koyo Gunkan records that Masatoyo was never given a special commendation for his services - and some have suggested that he opposed Shingen's handling of the 1565 Takeda Yoshinobu affair. He was recorded as having 250 calvalry under his command. Masatoyo was said to have been both handsome and good-natured.