Momonga is a regular salaryman who leads a guild in an DMMO-RPG known as Yggdrasil. After twelve years of playing the game, the servers are finally shutting down. Momonga logs in for the last time, seeing the game to its end. However, after the clock strikes midnight, nothing changes.

Grateful that they weren't cast aside, the floor guardians experience the rule of their true master for the first time. Momonga quickly assess the situation and works toward protecting the tomb from invaders while contemplating what he must do.

Momonga continues his efforts to protect Nazarick from the unknown forces he may be up against in this world. As he manipulates the Mirror of Remote Viewing, he notices a village being attacked and decides to test his strength against humans.

Momonga finds that the attackers of Carne Village were Slane Theocracy soldiers dressed as people from the Baharuth Empire. As the attack to lure and eliminate Gazef Stronoff continues, Momonga takes this chance to continue his tests...

Momonga sets out with Narberal disguised as humans under the names of Momon and Nabe for the city of E-Rantel. There they register to become adventurers in order to gain more information about this unknown world. As they do, evil gathers around them.

While Momonga has some doubts, he accepts Nphirea Balear's request under the condition that the members of the Swords of Darkness join them. Though her urge to kill keeps distracting her, Clementine continues to slowly find her way to Nphirea.