Toilet-Bound Hanako-Kun Vol. 6 (manga)

School Mystery No. 1's Clock Keeper of the future has gone out of control, turning Kamome Academy's entire student body into wrinkly old people! Hanako-kun, Nene, Kou, and Akane will have to work together to catch this agile trickster and keep the school from becoming a retirement home. But just when they seem to have Mirai cornered, one final prank goes horribly wrong, bringing Nene's secret out into the open...