I don’t really remember much. A guy looks regular, but he can turn into a demon by, vaguely remember this part, putting his thumb in his mouth and blowing. The pressure pushes his demon characteristics out. I think his boss actually turned out to be a demon as well, but more powerful.
It’s not much to go on, so thanks for any help.
May it be, Spawn?
https://youtu.be/WukhbpAhvrc
My Demon Lover?