In The Land Of Leadale Light Novel Softcover Volume 08

Cayna finally interrogates Opus, who's been busy with various clandestine activities. He tells her that during the Game Era, Event Monsters in the Brown Kingdom broke out of the system and took corporeal forms, resulting in a mass monster propagation. Those monsters have since been sealed away in an Isolation Barrier, but Opus can tell it's coming apart at the seams...hence why he's been searching for other former players reincarnated in this world. In order to protect the world of Leadale, the players must gather in the Abandoned Capital for one big decisive battle!