Black Clover: The Devil who saved the world

Asta, born with no magic power, his brother Yuno, born with Magic, born with everything a kid could imagine. Extreme talent, a four leaf clover tome. People who recognize him as a future wizard King. Asta? Born with nothing. No magic, no talent whatsoever. He grew up with Yuno during his childhood, always watching as he got everything and Asta? Nothing. During his short life that has been living in this world, he's been training. Not in magic, but in physicality. For fifteen years the boy had been training non-stop.

But what if Asta had run away, grown tired of watching his brother gain everything while Asta had not gained nothing. When did it start to show to the others around him that he had been.... going away? They didn't know until one night, he wasn't at his training spot underneath the giant skull that was the demon.