what about consentual butt sex?
serious question.
Um... *Checks Rick Santorum twitter feed* I reserve my right to withold moral judgement owing to limited life experience. That's my serious answer. I'm an ultraconservative, but I can't pass judgement without a scripture to back me up.
This said, butt-sex in any form does not make for a good plot highlight in a VN.
Especially when character recieving said butt sex is a Burial Agent... which... basically... makes her a Catholic. *Awkward pause* I mean, this (Tsukihime) was the same game where Arcueid Brunestud, the nice lady vampire, sent you a familiar in the form of your sister-who-isn't-actually-your-sister-in-the-usual-anime-plot-twist... for you to shag. For some interesting reason, the Tsukihime anime (Lunar Legend,) was devoid of butt-sex. And faux-incest. Actually, pretty much all the sex got cut.
edit: now I feel bad. Underage kids come on this site, don't they? I should be more careful what I post. We all should.
edit 2:
Look - someone's already making a KS fangame.
www.desura.com/members/fundoshigames/blogs/hanako-dash-freeware-fan-game
You'll have to copy/paste link. It's 4:21 AM, and I can't see straight, much less remember imbed tags.