The Misfit of Demon King Academy, Vol. 1 (light novel)

Tyrannical demon king Anos Volidgoad has destroyed humans, spirits, and gods alike, but eventually tires of endless war. Dreaming of a peaceful life, he reincarnates two thousand years into the future, only to find his descendants weak and complacent, and modern magic a joke. But when he enrolls in Demon King Academy hoping to regain his former glory, he's labelled a failure and a misfit! What's going on with this world?