Ukitsu

Visual novel version
He is Saji's partner. He is the one behind Sōsō's brainwashing and Shuyu's betrayal so they can kill Kazuto.

Anime version
A mysterious figure with magical powers. He gives the Chō sisters the magical book known as the "Crucial Keys to the Way of Peace" (太平要術, Taihei Yōjutsu), allowing them to create "magical microphones" in order to jumpstart their careers as idol singers. It is not known at the moment what his real motive is but it appears he using the Chō sisters to make the book gain large amounts of magic. When the Chō sisters reject the powers of the Crucial Keys to the Way of Peace, thus ending the Yellow Turban rebellion, he takes back the book from them before Kada could destroy it.

(Source: Wikipedia)