**Height:** 167 cm
She is a childhood friend of [Raku](https://anilist.co/character/48393/Raku-Ichijou) as well as his current homeroom teacher. Yui is also the head of the Chinese mafia group, Char Siu. Yui is also in possession of a fourth key but has confirmed to Raku that she is not the girl he had made a promise with ten years prior.
