Manadeshi ni Uragirarete Shinda Ossan Yūsha, Shijō Saikyō no Maō toshite Ikikaeru

Freed, a middle aged hero, defeated the Demon King after a deadly battle. However he is killed by his beloved disciple who tried to monopolized all the credit. Immediately after that, Freed somehow came back to life as the new Demon King. The Demon King’s castle is on the verge of being overrun by the oncoming heroes. His second-in-command, a beautiful girl from the demon tribe, and his subordinates try valiantly to protect him. In order to save them, Freed unintentionally ends up fighting against the heroes. The former hero becomes the most powerful Demon King in history, and a great counterattack to save the demon world on the verge of destruction begins…