Kohinata Riko's love interests are very low. However, she doesn't want to admit it, and knows there's no way she'll be able to admit it, so she keeps it to herself for a long time. One day, while she was having a study session at her classmate Tomoka's house, a girl with a school bag appeared in front of them! It turns out that Tomoka has a younger sister who is still in elementary school. Riko feels like time has stopped because she's so cute, but it seems like the sister has some hostility towards Riko...? A high school girl who has pedophilic urges for children and a girl who wants to become an adult...