Memphyz's manga / #Archmage(1)

48 in the original timeline the OG Hero was an idiot who was arrogand, stupid, and his decisions led to more casualties. He died, dooming everyone since he had the unique power to kill the demon god. So the mage attempts to rewind time before he dies. And he wakes up 20 years previously and this time will fix it. He had been a hero candidate before, but gave it up since he felt he was not worthy.