Bit of a cunt move for a prank, honestly speaking, if you consider the ramifications of it being seen and the subsequent rumors.
It was actually a prank by her younger sister.Onee-chan, I think it's best if you don't sleep with your ass out in the open.Phew... That makes this the 7th time...Could it be that the serious-looking class prez is secretly...!!Tallies on her ass...!?