metroanime
Twisted, the Board Game
Series: Ranma, Spells'R'Us
Sex factor: fairly high
Kink factor: magic, f/f, BDSM, transformation, all KINDS of weirdness
The Ranma cast is trapped playing a magical game with mystical penalties for winners and losers alike. The actual sex tends to be more referred to than explicitly played out, but this is clearly a sex-centered story. Multiple endings.