Yousui (Yong-Shua) is one of the four demon gods. He was under the command of Tenkou in OVA 2/Volume 17.
The demon god's true form is never shown, as Tenkou gives him multiple bodies to inhabit to deceive the Suzaku Warriors.
When he takes the form of Tamahome, he looks exactly like the warrior but with slightly longer hair to signify the passage of time. When he stops pretending to be the warrior, his eyes become dull and menacing.
His pseudo-demon god form, he has light brown hair that stands up on end and purple markings on his face and forehead. He also possesses a staff.
In Volume 17, Yousui is the last of the four demon gods to appear. He takes on the likeness of Tamahome and allows Tasuki to find him riding in the forest.
To further his deception, with his powers of puppetry, Yousui uses a vacant body to pose as his demon-god-self and attacks the company. "Tamahome" easily disposes of the puppet using the powers Tenkou gave him and, with help from the Jewels of Memory, convinces Miaka and the others that he is, indeed, the real Tamahome.
Taka accepts that Miaka will stay with this Tamahome in the world of the book and returns to the Real World. While in his apartment, Taka stares at his reflection in a mirror, contemplating Miaka's love for him and the amount of time he has before he vanishes. Suddenly, Yousui, still appearing as Tamahome, appears within the mirror. He warns Taka to never return to the world of the book and that Miaka belongs to him, now.
Then, Taka teams up with Keisuke, Yui, and Tetsuya to do further research. In the book, Yousui begins to seduce Miaka but she feels that something is wrong and she cannot erase the memory of Taka from her head. Meanwhile, Chiriko has his suspicions and rummages through "Tamahome's" bag. He finds the Scroll of Seiryuu and a marionette in the likeness of the demon god that "Tamahome" killed earlier.
Taka calls to Miaka, who decides to be with him, and she returns to the real world, leaving Yousui's plan a failure. When the Suzaku Seven ask "Tamahome" where Miaka went, Yousui drops the act and uses his powers to tie up the group with marionette strings. Just when Yousui starts to transform Tasuki and Chichiri into his puppets, Chiriko bursts in with the scroll and restrains the demon god, weakening the strings long enough for the two living warriors to escape.
Then, Taka and Miaka enter the book to face off against the demon god. Chiriko correctly assumes Yousui wanted to deliver the scroll to Tenkou in order to seal Seiryuu away like he would Suzaku. After warning them that they will perish if they fight Tenkou, Yousui vanishes.
Yousui appears again at the Konan Imperial Palace while Tenkou makes his assault on the grounds. He traps Miaka and Taka behind an impenetrable demonic barrier and attacks them both. Miaka, using the last of her strength, shields Taka from Yousui's life-force blast.
Taka rises and, just as Yousui prepares another strike, he embraces the demon god. This causes an explosion that damages Yousui's Tamahome puppet. As the puppet falls limply to the floor, now without a host body, Yousui dies and Taka regains all of his memories. Taka emerges from a glowing red light with the mark of the "ogre" on his forehead, prepared to fight Tenkou.