KissXSis (2010) : 1x9

As Keita tries to study, Ako and Riko compete with each other to be the most helpful. Whilst alone in the room, Riko and Keita end up doing some 'footplay' under the kotatsu until Ako catches on. Whilst looking up on good luck charms to help Keita with his studies, Ako and Riko learn of one that is made using pubic hairs. After much deliberation, the sisters pluck their own hairs to make the charm and give it to Keita, convincing him not to look inside. Keita takes it to school with him, though Ako and Riko are understandably embarrassed.