Age: 25
Birthday: February 26

Aoi and Akane's uncle and legal guardian. He's a television announcer.
When the twins' mother died, their father (his brother) abandoned the twins in his care and ran away. Because of that he broke up with his ex-girlfriend Megumi. He later takes Shiharu in as a babysitter.

Seiji falls in love with Shiharu but tells her that she should become a proper adult before she decides whether she will go out with him or not.

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