Yui is a young teacher who has just started her career at Kisaragi Academy. She is cheerful and friendly to her students, especially to Ayumi Shinozaki, who compares Yui to a sister, and plays pranks along with her. Even though she is enthusiastic, she believed that she was a bad teacher, until Hajime Yamazaki explained to her the true meaning of teaching. Throughout the events in Heavenly Host, Yui proves to be a brave and determined individual that deeply cares for her students, even more than herself.