愛弟子に裏切られて死んだおっさん勇者、史上最強の魔王として生き返る (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…