Yamakawa ryu (or Kawa for short) was born a warrior, the son of possibly one of, if not the greatest swordsman in the world and a hasira, at least until he ended up getting poisoned by a demon and became too weak to remain one, Kawa was taught at a young age about the demons that plagued their world, about how they fed on human flesh, how they retreated from sunlight, one of their few weaknesses, Kawa wanted to grow up to become as strong as his father protect people, but one night a stranger came to their door, a man who introduced himself.....as muzan, kawas father died that night giving him time to run with only swords in his arms, giving him instructions to go and find a friend of his, a man who would teach him.....how to become a demon slayer, join Kawa on his journey as he meets new friends, faces fierce demon foes, finds love in expected and unexpected places, all on his journey.....to kill the demon who killed his father.