Qual

Known as the "Sage of Decay," he was a demon who served under the Demon King and committed heinous acts until he was sealed by Himmel and his group. Among the Demon King's army, he was a leading magician who developed the first-ever piercing magic, called Zoltrak, which could kill people, and he slaughtered numerous adventurers and magicians. His strength was so great that even Himmel and his group could barely seal him, and Himmel himself came annually to check on the seal.

When the seal was broken, Frieren and Fern set out to subdue him, but he immediately analyzed modern magic, identified its weaknesses, and devised countermeasures, showing power befitting the name Sage of Decay. However, for Fern, it was just ordinary attack magic and was completely sealed, and after 80 years, Frieren struck him down with Zoltrak. He was called an old friend by Mahato of the Golden Land, one of the Seven Collapse Sages.