Forgot the title of the story

I read this story some time ago so I don't really remember much. What I do remember however is that the main lead was a soldier when the devil-like creatures had an outbreak. When deciding who to send back in time in order to prevent it however he was forced to go since the hero wasn't able to go. While going back in time, he went insane due to how empty it was? I'm not sure but I do know that when he awoke he was at this academy, overpowered, and killed this noble who was harassing him.

Thank you towards anyone that may be able to help me.
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