Well if he actually made a contract with the Demon King himself, the old geezer would just be like :*holds microphone while sticking his pinky out* "A contract, duh? Yeah i guess i might've been bored and done something like that once, but who knows!"
I actually approve of the fights in this manga, they're quick, most of the time funny, and cut to the edge appropriately.
Oh and they look awesome and not the least bit confusing due to some rlly bad artwork (like in the big 3 D