Iroha ni Konpeito

Chako and Tatsu have been friends since childhood, as they have grown in the same apartment building complex. However, they haven't talked to each other as much since the third grade. As high schoolers, they end up in the same class, but Tatsu remains as cold as ever towards Chako. But then, one day, Chako's friend confesses her feelings to Tatsu and he readily accepts her! But Chako is left visibly shaken after that!