Yui is a young teacher that just started her career at Kisaragi Academy. She is cheerful and friendly to her students, especially Ayumi, who compares Ms. Yui to a sister, and plays a prank along with her. Even though she is enthusiastic, she believed that she is a bad teacher. 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. She is 23 years old.