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 in this game world, Shuutarou decides to switch 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! Which of his six faithful boss minions will he pick?!