An UTAUloid and genderbent version of Yurika Sayu. Though it seems to have branched off, so Sai is considered a twin of Sayu.
His hair and eye color are the same as Sayu's. Fans draw him in a blue Chinese robe with black pants. And his voice is described as being similar to Kaito's.
サイ君にマイマスターを歌ってもらった (sai kun ni maimasuta^ wo utatte moratta) (I sing to you My Master) - Yurika Sai
