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

A CITY BATHED IN BLOOD AND CHAOS!The Survivors have failed in their mission to guard the idol concert. Diamond's main body has been broken. Karan has fallen victim to an incurable curse, and with Garos dead, they have no clue how to help her. As if the situation isn't dire enough, Argus, the leader of Combat Masters and Nick's old mentor, appears before him, but not even Union is a match for Labyrinth City's most powerful warrior. When an ally arrives, it seems the Survivors might be able to turn the tables…However, any hope is shattered when Callios, the Sword of Tasuki, joins the fray leading an entire pack of White Masks. Is this the end for the disillusioned adventurers?!