Kuro no Majutsushi -Ore dake Cheat Skill de Kaiki Shita Chouetsu Majutsushi-

Rei Kurosaki is a “colorless” in a world where one’s worth is defined by the color of their mana. With no magical skill of his own, he spends years as nothing more than a porter for his talented but arrogant younger brother Kai. That is, until a raid against Chronos, the God of Time and Space, wipes out his entire party. On the brink of death, Rei awakens a hidden skill that allows him to steal skills and rewind time itself. Sent back to the past, Rei begins again with knowledge of what is to come and a power no one else possesses. As Rei levels up at an unprecedented rate, he must prepare for the eventual return of Chronos while dealing with those who once treated him like trash.

Original Webtoon

Official Translations:
Korean: Naver Webtoon, Naver Series
Others: English, French