It's not because she's a faunus, though.  It's because she's legitimately insane.  The only reason she hasn't been stuck in a straightjacket and thrown behind barns is because she's been hiding it well.

If the excuse all this time was that it's because she's a faunus, then that's bullcrap, not usable.

Since she's going to be sent to an asylum or worse if this ever gets out, if Kaben wants to continue playing Mokuren, he won't ever be able to reveal her secret to any fellow students.  And the cannibalism will only ever exist because Kaben thinks its fun, not for enhancement or interaction or anything.

My allowing it to be an exception is the only thing that allows it to exist.  If it keeps coming up with such regularity, it's going to get discovered (potentially by GM powers), and Mokuren's going either to a sanitorium or into the ground.  I'm allowing it to exist, but by existing in a capacity where everyone can continue to RP normally, it's essentially meaningless.