If this is indeed Nana to Kaoru; is it possible this is that Class President (I think... if nothing else the dude who liked the fem-dom-pegging video) guy's sister? I read on a board how he and Kaoru ought to give her a few 'lessons' in what an M feels like; considering how she mistreated her brother. (Also; this doesn't really look like Tachibana... to me at least...)