At a fictional high school, Makoto Ito becomes enamored with Kotonoha Katsura, a fellow commuter. With the help of a classmate, Sekai Saionji, they start dating. However, Sekai's initial matchmaking joy turns to jealousy as she harbors her own feelings for Makoto. One day, at the train station, Sekai impulsively kisses Makoto to repay a perceived debt, leaving him stunned before departing cheerfully.