Saitō Kiheiji was an individual during the Sengoku period.  He was the third son of Saitō Dōsan.  His mother was either Miyoshino or Omi-no-kata.  He resided in Inabayama Castle along with Dōsan and his older brothers, Saitō Yoshitatsu and Saitō Magoshirō.

Along with his next older brother, Magoshirō, Kiheiji was taken well care of by Dōsan, and given the name of Isshiki Uhyōe-taifu.  This bred arrogance among Kiheiji and Magoshirō, who gradually came to despise their older brother, Yoshitatsu.  In 1554, Yoshitatsu succeeded Dōsan as head of the Saitō family, but in anticipation of being removed from the line of succession, Yoshitatsu had devised a plan.  On 11/12 of 1555, Yoshitatsu feigned illness and called Kiheiji, Magoshirō, and others to an inner room at Inabayama Castle.  After Kiheiji and his older brother, Magoshirō, became intoxicated with drink, they were murdered by a close retainer of Yoshitatsu named Hineno Hironari (Bitchū-no-kami).

Under an alternate theory, only Magoshirō was killed by Yoshitatsu while Kiheiji survived and became known as the younger brother, Toshitaka.  This theory is subject to question and the two brothers are deemed to have been killed at the same time.