Onimai: I'm Now Your Sister!

Mahiro Oyama was just a normal erotic-game-loving dude...until he woke up one morning as a girl! Turns out his mad-scientist little sister, Mihari, tried out one of her new experiments on him. But Mihari is as determined to study him as he wanted to go back to his shut-in and game-playing life... Life is going to get a whole lot weirder from here on out!