(In the past) The heroes finally did it, they did something no one has ever done. They had defeated and destroyed Black Hat, the demonic entity that plague their lifes for centuries. Black Hat Organization had fallen into ruins and villains went into hiding because no demonic entity was there for them to hide behind, to help them destroy the heroes who ruined their evil plans. The heroes celebrate.....but they didn't know the truth that he wasn't truly destroyed, just his physical body was. His demonic soul was still alive and hiding in the Black Hat puppet (he hated that thing with a passion but it had come to a good use now) that was thrown aside without a second thought, waiting for an unfortunate soul to pick him up.
It was a few weeks later when he was finally found, you were brave enough to look through Black Hat Organization ruins. Picking through it to find cool stuff that was left behind or abandoned, you moved closer to where he was thrown away. When you saw him or to say his puppet, you picked it up and laughed a little. It looked so harmless and goofy, you place it in your pocket and carried him home. Once you made it home, you carefully clean him up before putting the puppet on. An innocent game turns into a deadly trap immediately, you scream in pain as it felt like something was burning you as it digs itself into you. The Black Hat puppet falls to the floor as he infected you like an parasite, latching onto your soul as he forced the bond between you.
( Present Time) You don't know how long it been now as his soul and yours had become one, that you become his vessel and host. You still look like you but different in a way only a rare few people can see, your left eye was gone. Just a empty void from him eating away at slowly over time to complete the ritual (sacrifice of flesh and blood), you now wear a eye patch to hide it. Your shadow was replaced by him, to the blind eye it looks normal but to you. You can see him, hiding in plain sight. He didn't have physical body but he could see hold a form near you for others to see (but it takes a lot of energy out of both of you) or only for you to see him like a cruel ghost, either way he still had power over you. The Black Hat puppet sat there in a glass case on your bookshelf as a reminder of that day, the day Black Hat claim you as his vessel.