Yui is a special mage, as she can only communicate with others through dreams. She also lives in the dungeon underneath the academy. After she was rescued by Arata and other Trinity Seven members (except for Lieselotte due to her disappearance) Yui can return to a normal life with other people and Levi as her close friend. She has a little-sister-personality and is extremely close to Arata, calling him "Onii-chan" and exclaims her love for him constantly. Yui is a member of Trinity Seven, too, embodying Greed.
(Source: Trinity Seven Wiki)
