Another classmate of Ritsuka's. He is shown as being socially awkward and with low self esteem, and feels great jealousy towards Ritsuka. Yayoi admits that he loves Yuiko, but when he confessed to her he was rejected. Yuiko claims her reason was that she only dates boys taller than her, but the truthfulness of that statement is called into question when it is painfully obvious she loves Ritsuka, who is just as short as Yayoi.

Despite his jealousy of Ritsuka's close friendship with Yuiko, he is encouraged by Ritsuka's adamant claims that their relationship is purely platonic. He makes a firm statement he will not give up on Yuiko, and spends more time with her than ever.

It is notable that in the manga, Yayoi has a rather small role. He is absent for large parts of the story, and has only a small amount of dialogue. In the anime, they utilized his character much more to enhance the would-be love triangle of Yayoi + Yuiko + Ritsuka, and to inject comic relief into a dark story.

(Source: Wikipedia)