In charge of the Civil/Public Administration Department and has been head of the Kou family for nearly fifteen years. He is Shouka's younger brother, Shuurei's uncle, and Kouyuu's boss as well as adoptive father. He said his reason for adopting Kouyuu was because his older brother adopted a child so he wanted to adopt a random child to share his brother's experience. Although, Shouka revealed to Kouyuu that Reishin thinks of him as his own child. He's good friends with Kijin since he's allowed to be around him when he's not wearing a mask. He's also the one making all those different masks for Kijin. Kijin describes him as being crafty, coolheaded, and cold hearted, but Reishin is usually seen very cheerful, easy-going, and sometimes childish. He sometimes plays tricks on other officials.

Reishin is known to get carried away with things easily, going overboard with nearly everything (such as when Shuurei becomes ill and Reishin brings over just about every kind of medicine available, regardless of its relevance). Also, despite having difficulty finding the courage to tell Shuurei of his relation to her, he is shown to be an extremely protective uncle, going so far as to throw his fan (with clear murderous intent) at Ryuuki when the emperor attempted to articulate his desire to win over Shuurei's affections. He also requests that Shuurei call him "ojisan" which is used to address an uncle (or simply a middle-aged man), so as to avoid having to give his name.