The Unimplemented Overlords Have Joined the Party! Novel Volume 4 was written by Nagawasabi64.

Upon achieving the highest-tier summoner class, Shuutarou reunites with Crest's Party 7, who welcomes him back with open arms and a bit of shock. Just as the party prepares to take on quests and join the front lines, something is amiss in Calloah Castle Town. A man named the Liberator claims that players can safely log out from the death game that is Eternity, and that he's even done it himself! This revelation astonishes the players who have had enough of this world…and that's when the Liberator accuses Crest of being responsible for the ensuing chaos!