Siereis - I assumed it would be freeform. Like you said, the antagonist(s) could be the one keeping the plot moving. The demon and the faculty member could be moving at separate paces - such as, once the demon(s) gets a foothold in the school, he/she/they could start making trouble of his/her own outside of whatever the staff member's plot may be.
If a GM is wanted, though, I think we can work something out.
I just watched the movie today and, you're right, there was some sexiness to the whole thing but no actual sex. Mostly it was panty shots, a little kissing and a few topless scenes. I do not mind at all stepping the sex up in the game. I think it would work well, particularly if we set up separate threads for private interactions. (Like 'so and so's bedroom' in a oneshot for a particular scene, for example)
My own preference would be no actual rape scenes involving my character, but I'm open to mind control or altering (like drugging) and force. I just can't get my head past the rape in my writing, it's a personal weakness -.- It does not, however, bother me if others choose to have a private non-con scene involved in this game - if that makes sense?