There was once an oni mother who gave birth to a human-looking child. Instead of an oni's horn, this child was born with a sword in hand called the "Onigirimaru" or Oni Slayer. He has no name and is only referred to by the name of his sword. Though he appears human, he is pure oni.

Believing that he will become human once all of his kind vanished from the world of humans, he sets out on his destiny to slay all of his kind. Even now, in the mother world of Japan, he is still out there slaying oni.