She was originally sealed into a dungeon but her friends get her out of there. Yui has a very happy and bubbly personality, which often makes her seem childish at times. As such, she is very open with her thoughts, almost always expressing her feelings vocally and physically. For most of the time, Yui is usually excited and joyful. Yui's Thema is Amicitia from the Avaritia archive, and her magic is Arc Symphony. As a Cardinal class mage, she is one of the strongest mages in Biblia Academy.