Apparently, Disillusioned Adventurers Will Save the World, Vol. 5 (light novel) — Shinta Fuji

The Survivors failed in their mission to guard the idol concert. Diamond is gone, and Karan has fallen victim to an incurable curse. And unfortunately, with Garos dead, they have no clue how to help Karan. When Argus, leader of Combat Masters and Nick's mentor appears, even the Union spell is no match for Labyrinth City's most powerful. However, with the help of a certain someone, it seems they might just be able to turn the tables...until Callios puts the Survivors in an even more desperate situation. Is this the end for the disillusioned adventurers?