The God-Slaying Demon King 03

Hiram, the strongest demon king in history and ruler over all of demonkind, refused to obey the demon god's demand for sacrifices. A fierce battle ensued, which ended with Hiram losing his life. Five centuries later, Hiram successfully reincarnates himself as a young human with his magical powers intact. After an assassination attempt while visiting the Kingdom of Orteville, Hiram uncovers a ploy by the chancellor, who has designs on enhancing his power. But a shocking metamorphosis reveals the chancellor to be nothing more than a pawn being controlled by an old nemesis.

Volume 3 of The God-Slaying Demon King manga series by Ezogingitune.