The Middle-Aged Hero Who Died After Being Betrayed by His Favorite Disciple Is Reborn as the Strongest Demon King in History

Middle-aged hero Fried defeated the Demon King after a fierce battle.
However, he is killed by his beloved disciple who tries to claim all the credit for himself.

Immediately afterward, Fried is somehow resurrected as the new Demon King.
The Demon King's castle is on the verge of falling to the approaching heroes.
His beautiful demon daughter and subordinates try to protect Fried bravely.
In order to save them, Fried unexpectedly finds himself fighting against the heroes.
The former hero has become the Demon King with the strongest power in history, and a great counterattack to save the demon world from destruction begins.