I Became a Magical Genius After Regression

Randel, the Talentless Mercenary Mage.

On the verge of death in an unknown ruin…

“I’ll save you. In return, I want 10,000 lives—” “Get lost.”

Crack!

He shatters the ancient artifact spouting nonsense
and returns 30 years into the past.

And then…

His casting time for magic became one second.