Tougen Anki

Shiki Ichinose, a young gun enthusiast, is living a carefree life until he's expelled from school. He's subsequently attacked by a man, but his adoptive father Tsuyoshi intervenes and saves him. Tsuyoshi reveals that Shiki is a descendant of the Oni, a powerful but destructive species that once clashed with the Momotarou lineage, of which Tsuyoshi and their pursuer are a part.