Koibito wo Netorare, Yuusha Party kara Tsuihou sareta kedo, EX Skill "Kotei Damage" ni Mezamete Muteki no Sonzai ni. Saa, Fukushuu wo Hajime you.

Chrome was a magician in the hero's party. He fought the Demon Lord's army alongside people like Irina, the lover who vowed to marry him in the future, and the hero, Yuuno, who was his close friend. They were all close companions. However, that was only in Chrome's mind. His lover, Irina, became intimate with the hero, Yuuno, and Chrome was sacrificed to make the hero stronger. Chrome's magic powers were snatched away and he was kicked out of the party. Demons surrounded him as he was on the verge of death and he was driven to a corner. At that moment, Chrome awakened to a "darkness" within himself. Amidst his despair, he acquired an unrivaled skill. Now with this skill, he could exact revenge. (Source: Shousetsuka ni Narou, translated)