An old hero who died after being betrayed by his beloved disciple comes back to life as the strongest demon king in history (Associated Names)

Freed, a middle aged hero, who defeated the demon lord after a deadly battle. However he is killed by his beloved disciple who tried to monopolized his credit. After that, Freed was somehow revived as new demon lord. The demon castle is on the verge of being attacked by the approaching heroes. The beautiful adjutant’s…