Sui is Keis younger brother and resembles a younger version of Kei. Initially he dislikes Kei because he finds living with him disgusting and thinks of him as a robot wearing human skin. Because Sui feels very inferior to his brother who is good at everything he believes that he cannot reach Keis level and he refuses to take his studies seriously. However when he sees that even his quotperfectquot brother can become desperate and caring Sui develops a huge brother complex. Sui likes to call Hikari quotStupid Girlquot but approaches her frequently when he thinks that Kei needs help. He is in grade 6 class B at Hakusenkans elementary school division.