I believe that Sanguini is actually Lestat in disguise. It's a perfect Lestat sort-of prank, calling himself 'Sanguini' (blood, HA!) and parading around some wizarding boarding school, looking for young-girl blood to suck.
But now that I've posted this, we all must watch out, because we're bound to get some Mary-Sue fan fiction out of this starring Sanguini. It'll be Mary-San. And there will be anime pictures to accompany said stories.