Takahiro Katagiri

Takahiro is Tatsuya's best friend and classmate, inspired by his intelligence. He readily offers help when Misato needs to study and, seems to have developed romantic interest on the girl before they had even ever met personally (thanks to Tatsuya's descriptions of his little sister).

[Chapter 3, 8th page — Author's Note] According to Shiina Ayumi, Takahiro was originally meant to have "split personality" like "Jekyll and Hyde". When she showed the outline of the story to the editor, they said it had "too much badness" and after thinking about it, Shiina discarded the whole original story. That is the reason this manga's title has nothing to do with it's content.