The Butcher

Short-story.

Connected to the world the Sun Warrior stories are in, or at least one of those stories was in. It's also inspired by "The Butcher" from the Green Lantern comics and the idea that it can inhabit a host. Jinchuurikis from Naruto were also a source of inspiration. So yes, the main character has a powerful being sealed inside him. That's all I'll say.