Yuu Nikaidou is a former employee member of Easter. In order to find the Embryo, he joined Seiyo Academy and became in charge of Amu Hinamori's class in the guise of a ditzy but kindhearted 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". Yuu has orange-brown hair and wears glasses. When Yuu is in disguise he talks sweetly and is extremely clumsy. Yuu's normal-self talks seriously. During his time at Easter, he only wore glasses at school. After he left, he began wearing them permanently. He normally wears a white shirt, suit, and tie.