From the studio that brought you Death Parade, Parasyte, and No Game No Life comes a series that takes place in the world of Yggdrasil, an MMORPG that's scheduled to be shut down permanently. With no family or friends outside the game, veteran player Momonga refuses to log out. As the servers go dark, he discovers that the world inside the game continues to change as NPCs begin to develop personalities and minds of their own. With a new world at his fingertips, Momonga decides to use his power and skill to take control of Yggdrasil and become its overlord.
Momonga finds out that Shalltear has revolted against him, due to something that had happened while she was on her mission with Sebas and Solution. The story rewinds a bit and goes over that very event. What could possibly change her loyalty to him?