Peerless Reincarnated Demon Lord in Hero Academy summary:
Aldnoah, the Demon King, takes his own life in front of the heroes and is reborn in the world a thousand years later.
In order to see if humans have become strong enough to stand up to the Demon King, Aldnoah, who has grown into a young man, decides to attend the Academy for Heroes....
This is a story of a former Demon Lord's rise to become the strongest!