As an infant, the boy Edel fell into the Demon World. Luckily, he was found and raised by an old man.

However, when he turned twelve, his adoptive grandfather passed away.

Following his grandfather's dying wish, he set off to find an acquaintance of his grandfather residing in the Human Realm.

That acquaintance was none other than the hero Maribel, revered as one of the Four Heroes.

Subsequently, thanks to Maribel's arrangements, Edel began attending the Hero Academy.

However, he was unaware.

That the Demon World where he was born and raised was an incomparably harsher environment than the Human Realm.

That his adoptive grandfather was a legendary grand sage, affectionately called "Sensei" by the Four Heroes.

And that he himself had acquired unimaginable power, having been subjected to rigorous Spartan training by his grandfather in the brutal Demon World.

"Huh? I encountered Bahamuts frequently in the Demon World, though? I even kept them as pets."

"Bahamuts as pets?! Th-those are Super S-class monsters! ...Sensei, you've certainly left us with an extraordinary child..."

--It seems the Human Realm is far too easy for someone raised in the Demon World.

*This work is also published on Kakuyomu.