Yasuko is a popular third-year senior at Matsuoka Girl's High School. She is a cool upperclassman and the captain of the basketball team, though Fumi mistakes her for being in the Literature Club when they first meet. She has almost a star status in Matsuoka and Fujigaya (more so in Fujigaya).

She insists on involving Fumi in her visits to Akira's school. Her initial reason was to pawn off the role of Heathcliff to Fumi who is almost as tall as she is, but Yasuko soon grows a deeper interest in her.

After visiting Fujigaya Girls Academy and rejecting Kyouko's confession, she asks Fumi out, who accepts.

Yasuko enjoys the arts immensely, as she is shown being a very good artist, is an exceptional actor and reads profusely. Her accomplished aura could be a result of the subconscious conditioning she received as a child. Being the youngest Sugimoto sister, she often had to listen to the praises that Shinako, Kazusa and Kuri received.

Despite being seen as personable and likeable in public, Yasuko is unintentionally bratty and sullen at home and is often in contention with her third eldest sister Kuri who provokes her.