ONIMAI: I'm Now Your Sister! 5

This brother has girl power of monstrous proportions! Former twenty-something shut-in Mahiro Oyama was transformed into a girl by an experimental drug, and now he's celebrating birthdays, buying bras, and even turning heads as his exploration of how the other side lives continues! But when the drug starts to lose effectiveness during swim class, can he get to safety without anyone noticing he's not really a she?! The brother-turned-beauty's schoolgirl life faces its greatest crisis yet!