Been a while since I read any Harry Potter, but I'm guessing the bunny girl is Luna Lovegood. But then who is the lion-haired one? Not sure if I get the joke here. Is Lelouch the Half-blood Prince referred to here, because his mother wasn't a noble? And is Hermione slapping Harry for chumming up with a Slytherin (Lulu's green and yellow cape)?
Actually, this is Tom Riddle cosplaying as Lulu. This is because the first sentence of the speech bubble says "Tom Morv--(cut off) commands you!" It's been a while since I read Half-Blood Prince myself, so I can't say who the bunny girl is...though, if I -had- to take a stab at it, I would say Bellatrix Lestrange just because she's obsessed. I'm not entirely sure, though.