Mayuki's butler. Seiran was once called a "doll user" by Byakko during one of their encounters. He also is found occasionally in a secret base of some sort, where he can keep a close eye on Kyuto's happenings, as well as Mayuki's whereabouts. He belongs to the family of Shinano, a family that supports the Hyuuga family. He made a promise to Mayuki's mother that he'll always protect Mayuki.

Spoiler

He's Shien and Seiju's younger brother and Mayuki's uncle in reality.

(Source: Wikipedia)