A brief description of manga The Betrayed Hero Who Was Reincarnated as the Strongest Demon Lord
The hero by the name of Fried opposes a demon lord with his student, Lyle. Fried practically kills the demon lord in a fierce battle. “I am going to end this war!”. But when he was left to strike the final blow to the demon lord, his disciple, Lyle, betrays him by stabbing him right in the back. However, Fried, who is supposed to be dead, wakes up next to a girl, a demon who somehow calls him a lord. It seems that Fried has risen up as the new demon lord and now will have to protect their race, fighting against his past comrades.