Apparently, Disillusioned Adventurers Will Save the World, Vol. 4 (light novel)

THE DEEPEST SHADOWS CAN HIDE BEHIND THE BRIGHTEST LIGHTS. After a fierce battle, Nick and the others succeeded in crushing the demon-god worshipper White Mask. The guild is extremely happy with their performance, so the Survivors are entrusted with Nick s dream job: guarding an idol concert! But when they discover counterfeit tickets and a connection to the demon god s adherents they start to doubt that this is a normal escort mission. And that s all before Sun Knight captain Alice shares her suspicions about Nick s former party member Garos, shaking him to the core. Karan is there to lend her support, but her feelings for Nick seem to be changing...