Watadamashi-hen: Cotton-Deceiving Chapter, Part 1 - S1.E5

Keiichi and his friends attend a game competition at a Sonozaki family owned shop. As a consolation prize for the event money, the store owner gives dolls to everyone except Mion. Keiichi gives his to Mion as he sees no value in keeping it. Later, Keiichi and his father meet at the cosplay restaurant. There, Keiichi meets Shion and confuses her for Mion, due to similar appearances. She proclaims that she is actually Mion's twin sister. Keiichi believes she is Mion pretending to be effeminate.