KissXSis - Season 1 Episode 5 I'm Sorry!

While talking to his friends, Keita accidentally gropes his fellow student, Miharu Mikuni, and gets slapped. Ako and Riko become suspicious about whether Keita has been 'cheating'. When Keita goes to study at the library, Miharu, who is the librarian, becomes too intimidated by Keita to go to the bathroom. Before she can go to one, Keita tries to return a book she dropped and chases after her, dragging her into various hiding spots to hide from Ako and Riko. However, they end up getting locked in the gym storage room and their hashed escape plan leads Miharu to relieve herself on Keita's back. They eventually manage to escape and Keita promises to keep Miharu's incident a secret, though gets beaten up when he accidentally sees where Miharu had removed her panties from.