Kairos [Hero Reborn As The Demon King]

Ceron, the proclaimed hero of the Empire was on the verge of killing the demon king when his subordinates murdered him. Instead of finding himself in the afterlife, he finds himself trapped inside the body of the demon king he was sworn to kill. Now it is up to him to find a way to undo whatever dark magic is cast upon him, while hiding the fact of the reincarnation from the demon king's deadly generals.