Kiraware <Kuro Majutsushi> no Yarinaoshi: Yuusha ni Uragirare, Ryouomoi datta Seijo to Inochi wo Ubawareta Ore, Kako ni Modotte Subete wo

Moments before victory, dark mage Kai Austin is betrayed and loses everything. His death becomes a reset, sending him five years into the past—to the day of the class assignment ceremony—with all of his magic intact. Armed with max-level dark magic and every memory of the future, Kai refuses to let history repeat itself. This time, he will protect Colette, stop the coming disasters before they begin, and destroy those who once betrayed him. (Source: WEBTOON)