Yui is very active and expressive. She's a bit small, but she holds ranks in Karate, and even won tournaments when she was in middle school. She absolutely loves cute things, and her room at home is filled with fancy items. She always ends up insulting Aoki when he tries to approach her.
It is revealed that Yui was almost raped in middle school, thus starting to suffer from androphobia. Taichi helps her get rid of this phobia after she tells him about this incident.
She has rejected Aoki numerous times, but in his latest confession, she admits she is just not ready yet to have a relationship.(Source: ANN)