There will be more to him than that once I have a bit more time than that. I was thinking setting wise it would be Edwardian/Victorian-esque. Demons would be considered stories to tell bad children but as with now there are always people willing to 'dabble' or make fun of old superstitions and books and then sometimes bad things happen and no one knows why. Your guy for whatever reason could be at a party where the host is like 'ahahaha I raise demonz' and rather than leave you stay to watch his stupidity almost certain nothing will happen. Which it does of course and people end up dead but for whatever reason your guy doesn't. Maybe he was 'the virgin sacrifice' as part of the whole ritual or something? Who'd kill their sacrifice? Or it could be more sinister, a group of hardcore Satanists kidnap your guy from the streets when he's leaving a pub/work one night and honest to god try to sacrifice him to summon a demon, knives, cloaks, candles and so on. My demon prevents the killing of your guy but slaughters the others for whatever reason.

Yeah forgive the slime, pretend its not there :P it was the best demonic referance I could find for our Paimon. When his 'cs' such as it will be, goes up you'll see what I mean. He will have a human form though.