Ritsuka's classmate, Yuiko, appears ditzy and bubbly on the surface, but she is actually sharp and kind-hearted. On Ritsuka's first day at school, she is immediately fascinated by him. Encouraged by her mean-spirited classmates, she befriends him, though he is quite reluctant at first. As Ritsuka gets to know her better and realizes she is quite intelligent, they become good friends.
Yuiko and Ritsuka's friendship greatly irritates their classmate, Yayoi, who had been recently rejected by Yuiko. She claimed she only dated boys taller than her, much to Yayoi's sorrow. Despite this, Ritsuka insists that his friendship with Yuiko is purely platonic, which it indeed remains. However, in two separate confessions to Shinonome Hitomi, Yuiko professes her love and devotion to Ritsuka. Their relationship is close, but Yuiko's feelings seem to be a one-sided obsession.
In volume 2 of the manga and episode 4 of the anime, there is an incident where Ritsuka shows genuine care for Yuiko when she is bullied by her so-called 'friends.' They smashed a jar of homemade strawberry jam she brought for Ritsuka and demanded she apologize for breaking school rules. Ritsuka defended her, calling her bullies 'less than human,' which may have intensified her feelings for him. Unfortunately for Yuiko, in volume 4, Ritsuka abruptly leaves her to help Soubi, leaving her saddened as she recalls her efforts to become closer to Ritsuka without much success.
As the series progresses, an unusual yet harmonious friendship develops between Yuiko and Soubi. Despite their seemingly clashing personalities, they develop a unique understanding of each other.
In an early 2005 interview in the Japanese magazine Pafu, Kouga Yun stated: "She emerged when I wondered, 'What kind of girl would it take for Ritsuka to be happy?' While she was created to match Ritsuka, she changes from meeting him...with some injection of intelligence (laugh). She honestly wants to change to become worthy of Ritsuka because she likes him. So if Soubi wasn't around, they'd make a great couple (laugh)."









