Yuu Nikaidou (二階堂 悠, Nikaidō Yū) is a former employee member of Easter. In order to find the Embryo, he joined Seiyo Academy and became in charge of Amu's class in the disguise of a ditzy but kind-hearted teacher. His dream when he was a child was to become a robot engineer. However, when his mentor quit thanks to his ill wife and his parents told him they were against the idea, he lost sight of his dream and became a twisted person, though he recovered with help from Amu and Su. He resigned from Easter Company and officially become the teacher in charge of Amu's class. A running joke is that he calls Amu Himamori, the "hima" meaning "leisure time".