Sekai Saikyou no Fukushuu Shinkan: Kami ni Tsukaeshi Mono, Maou no Chikara wo Te ni Ireru

Raze was a prodigious priest who supported the legendary Hero. However, he was betrayed by the Hero with his party and sister being killed. He later absorbed the power of the Demon King and now seeks revenge on the Hero and the others that wronged him. (Source: KADOKAWA, translated)