Yuiko and Ritsuka's friendship greatly irritates their classmate, Yayoi. He had been recently rejected by Yuiko, although rather sorrowfully, claiming she will only date boys taller than her. Much to Yuiko's dismay, Ritsuka insists their friendship is platonic and it, indeed, remains that way. However, in two separate confessions to Hitomi Shinonome, Yuiko professes her love and devotion to Ritsuka. Ritsuka seems to trust Yuiko, despite his own issues with that kind of bond.
As the series progresses, a rather unusual, yet harmonious, friendship is struck between Yuiko and Soubi. Although it seems their personalities would clash, they have a unique understanding of each other.
Yuiko is characterized by her large breasts and considerable height. At 168 cm tall, Yuiko is much taller than Ritsuka and her other classmates and is often mistaken for being older than she actually is.