Sae Iwata is a slightly tougher-than-average girl. Her first love, Koki Kamishiro, was once a delicate and fragile boy, but now, in their third year of junior high, he has grown into a cool and popular young man. Although they have drifted apart, her feelings remain unchanged. When they are paired up to help prepare for the sports festival, Sae's long-hidden first love begins to stir once more.

Sae and Kamishiro end up in the same high school and class. Assigned to the same group for trash pickup, Kamishiro gets into a sudden argument with a classmate. As Sae steps in, he instinctively calls her by her first name, bringing back a flood of childhood memories. Meanwhile, another girl, Hisui, seems to be drawn to Kamishiro as well.

Knowing Kamishiro has a crush on someone weighs heavily on Sae's heart. Still, during their school trip, Sae finds herself unable to take her eyes off him. Her friends, Hisui and Kagawa, try their best to support her, but Sae always ends up showing her awkward side around Kamishiro.

Kamishiro admits to Sae that he has feelings for someone, describing his crush as "a star that shines brighter than the sun." The words pierce her heart, but she chooses to support him nonetheless. All the same, as Kamishiro continues to treat Sae just like always, she finds herself torn between her feelings and her resolve.

After the school trip, a class-versus-class jump rope tournament is set to take place, and Sae and Kamishiro are chosen to swing the rope. Despite the unexpected pairing, Sae tries not to be too conscious of Kamishiro. As practice begins, things do not go as smoothly as expected. One day after school, Sae spots Kagawa practicing alone behind the school building.

One day, Sae takes a day off from school. The next day, Kamishiro gets injured during club practice and also takes a day off. As they lend each other their notebooks to catch up on missed classes, they begin exchanging messages. A small incident leads Kamishiro to realize that Sae likes someone. Unaware of Sae's true feelings, he encourages her to go for it.

Kamishiro is selected as one of the main cast members for the class play. Struggling with his lines, he turns to Sae for help. As they rehearse, they make a promise to go see a movie together during summer break. On the big day, the class's performance is going smoothly until Sae suddenly bursts onto the stage.

With school events behind her, Sae throws herself into club activities. Just then, the date for her long-awaited movie outing with Kamishiro is set. However, a chance encounter with Kamishiro's cousin, Subaru, leaves Sae feeling uneasy, as something Kamishiro once said about his crush comes back to her.