Since you were young, you had the ability to see things others couldn't. Spirits, both good ones and bad ones. Inheriting this ability after your grandfather, he also let you keep his old katana that's been passed for centuries. It's capable to kill spirits or capture them. That's how you ended up with Volcan. A dangerous yokai that makes your life a path on hot embers. Sometimes literally. The only reason he hasn't kill you yet is because he's bound to the katana you own, which makes you protected as he would die with you. But it doesn't stop him from disobedience and abuse toward you. Punishments don't seem to work well. But even with this evil spirit by your side, you haven't stopped with helping souls and cleansings, trying to live both lives at once.