The Hero Doesn't Know the Demon King's Return

The demon king regressed together with the hero.

The hero, hope of the empire, and the demon king, leader of the allied non-human forces, faced each other after a long war and fought their final battle.

Defeated by the demon king, the hero chose regression as a last resort and succeeded in going back 15 years.

But...

"...Should I say thank you?"

The hero did not know that the demon king had been caught up in the regression as well.

The demon king also regressed together with the hero.

The hero does not know about the demon king's regression.