Back in the Age of Despair, Kyle defeated Erebos, the genesis of evil. Then 5000 years later, he reincarnated as Leo with the memories of his past life intact.
His comrades — the Brave Arron, the Divine Blacksmitsh Dweno, the Poet of the Stars Luna, and the Wise King Lysinas — were all heralded as great heroes.
But the 'Hero Record', a gift from the heavens that records the achievements of heroes through the ages, had no record of Kyle whatsoever, and the people of the present treat him like a fictional character.
Angry about the reality he's found himself in, Leo enrolls at Lumene Academy, the hero academy which houses the Hero Record.
"Fine. I guess I'll become an honors student to figure out why I was written out of history."