Okusama ga Seito Kaichou! S01E07 - Sneaky Student Council President

Rin and Kei Misumi move in next door to Hayato, who tries to keep his cohabitation a secret. Rin visits Hayato frequently, causing him to try to hide Ui. But Ui gets revenge for his not paying attention to her. Rin finally finds Ui's underwear and lipstick, and Hayato has to claim they are his to cover Ui, leading to a rather embarrassing misunderstanding.