Peacemaker (1991)

Tetsunosuke Ichimura has always been upset about his short stature. After he sees his parents being murdered by a Choushuu assassin right in front of him, he vows with all his heart to become strong enough to take revenge on their killer. It is now 1864, the first year of Genji. Tetsunosuke, now 15, heads to the headquarters of the Shinsengumi with his older brother Tatsunosuke, looking to join the historical group to fulfill his dreams of getting stronger. Little does he realize what he is about toexperience by doing so, for in order to join this army, one must forego his humanity and become a demon.