The Unimplemented Overlords Have Joined the Party! Novel Volume 2 was written by Nagawasabi64.

Shuutarou and his Evil Overlord pals made it out of Ross Maora Castle, but a spirit barrier is keeping them and the rest of Eternity’s players from entering a certain area. In order to progress further in this game world, Shuutarou decides to change character classes…from a swordfighter to a summoner! This way, he can call upon his six Evil Overlords whenever he wants. But being a summoner comes with its own caveats: He can bring only one overlord with him at a time?!