His obsession to find out the truth and jealousy towards Rin leads Yukio to join Illuminati. In the anime, It is changed so that he has the powers of Satan although this is not canon. He is voiced by Jun Fukuyama in Japanese and by Johnny Yong Bosch in English, while in VOMIC he is voiced by Ryūichi Kijima.

Does RIN get his powers back?

Shiro gains control at the last moment and sacrifices himself to protect Rin. Upon seeing this, Rin fights back by unlocking his demonic powers with Kurikara, the sacred sword in which his powers are sealed. At Shiro's funeral, Rin meets Mephisto Pheles, who agrees with his wish to become an Exorcist to defeat Satan.

Is Mephisto bad?

Mephisto is a perennial villain in the Marvel Universe, and is responsible for a number of evil acts, including capturing and holding the soul of Cynthia von Doom – the mother of Doctor Doom — until Doctor Strange and Doom freed her to ascend to Heaven. ... Mephisto refers to his domain as Hell.