I don't want to give the full idea away, as it is based on my novel I'm working on.
But it's dubbed Hell Boy Wonder and is an action/comedy superhero story with demonic possession.
The combat would be based on a more elaborate brawler like system that will allow you to basically create your on fighting style in a martial science like manner. Think something like God Hand, but more freeflowing. You'll be able to tap in to demonic powers such as spawning demonic weapons and magic spells in the midst of combat on the fly. You'll also be able to use your demon for devastating tag attacks similar to Vergil's clone moves.
The cast will be a pretty diverse, interesting, and even bizarre set. With a wacky main villain who possesses a sick sense of humor. Yes, the comedy would be dark and mature at times, but you can bet your ass hilarious. From the entertaining cutscenes to the in context taunts and quips shouted during mid battle, the game would have a great sense of humor.
While I would mainly love to create horror games, a fast and furious action game with comedic elements would also be a lot of fun to do.