Anna Koshiro has been friends with two handsome guys, Sou and Hinata, since childhood. She has a crush on Enamoto, a first-year high schooler, but she has difficulty finding a boyfriend as everyone always wonders about the relationship between Anna, Sou and Hinata.

One day, she goes to Sou's house and finds out that Sou has a girlfriend. She is not jealous, but she feels like she has lost him. On the other hand, Sou's girlfriend is upset about how Anna comes into Sou's room so freely and asks Sou not to let Anna into his room again. However, Sou disagrees and ends their relationship. Anna decides to overcome the odds and confesses to her crush. Enamoto accepts, but upon finding out that Anna has a boyfriend, Sou gets upset.

On their first date, Anna finds herself in her room with Enamoto. She tells him about something that happened in the past: She once had a chipmunk named Coco, and when it died, Sou and Hinata brought her another chipmunk and telling her it was Coco. Her mother had told her to treasure Coco as the two of them had used their own money to buy Anna another chipmunk.

Enamoto then shocks Anna by asking which one of them she likes. After she replies that the one she likes is him, Enamoto tries to kiss her but Anna gets scared. She wants to call for Hinata and Sou but she can't. They both suddenly appear after Anna kicks Enamoto away. Of course, she cannot continue dating him after what happened. Although she can't get what Enamoto asked out of her head, Anna is sure that the she will never be anything more than friends with Hinata and Sou. But what will happen when Sou confesses his love to Anna and asks her to go out with him?