Well, I've got an idea in mind that might be amusing to play. It has a its roots in Christian Mythology so I don't if you'd be willing to give it a shot but here goes a short description.
Recently an Angel has fallen from the grace of God and was sentenced to Hell. Upon being cast down it finds itself in the care of one of its old companions from before the war. It seems that the companion had made a deal with Lucifer to get its hands on the fallen one. Only to find out that the demon rebelled not because the it sympathized Lucifer, but because of the fact that it disagreed with God's policies about "He will be loved beyond all else." He just wanted the attention that the angel was showering on God.
I know this game sounds like it could focus mainly on sex, but I actually wanted it to focus more on convincing the fallen (Who is still clinging to its purity.) To join the demon in and assist it in ruling its layer of the abyss.
Now the real question would be "Why did the angel fall?" I was thinking that it was perhaps because of one moment of callousness on its part, where it essentially turned its back on a redeemed soul, because it was a horrible sinner before it returned to the graces of God.
I’d be willing to play either role.
Thank you for the time.