Angels are beings created by God to serve the purpose of protecting an assigned Human from unseen dangers (such as these Demons) and from poor decision-making. Guardian Angels, as people see them today (although they don't actually see them, except in rare near-death experiences). They're invisible to the Human eye, and can see each other, as well as the other unseen beings (dead people's spirits who have not gone to Heaven nor Hell, and other miscellaneous things along those lines, and other angels).
It depends on how descriptive we get with it. This RP will probably have some pretty morbid imagery (Instant "M" Rating) though this will more likely be demented creatures, explicit violence, and rather disturbing visuals. Probably setting the bar with graphic sensitivity by letting people go nuts with it.
So yeah, I suppose a soul-eating Succubi/Incubi would probably be more appropriate than a sex-crazed one. However, sexual gestures such as the kiss, maybe certain postures and other forms of seduction, though only to distract or lure away the Angel from its Human.
In other news, Solo finds love in probably the most predictable place ever.