The series begins with YGGDRASIL, a popular online game is set to shut down. However, Momonga, Guild Leader of Ainz Ooal Gown decides to stay and not log out while his friend Herohero has to log out and bids farewell to him. Momonga retrieves the Staff of Ainz Ooal Gown and proceeds to the Throne Room along with Sebas Tian and Pleiades.
Momonga sits on the throne, and modifies the setting of Albedo out of playfulness because it's the last few minutes till the shut down. When the clock hits midnight, the officially announced shut down time, he then notices that the server is still up and running. With his mind clouded in confusion, he then realizes that he still retains the outward appearance of his game avatar and tries to access the game functions like consoles but the functions are inaccessible. The next great shock comes in tow when he sees the NPCs of Nazarick begin to show sentience. In order to assess the situation, he orders Sebas to survey the outside of Nazarick while Albedo must assemble the Floor Guardians on the 6th floor.
Momonga teleports to the Amphitheater. There, he meets Aura and Mare and asks them to help in testing the Staff of Ainz Ooal Gown. He later summons the Primal Fire Elemental and even asks Aura if she wants to fight it, which she agrees and drags the unwilling Mare into the ordeal. The Floor Guardians then begin to arrive and they all swear their loyalty to the Overlord of Nazarick.
The episode contains examples of:
- The last day and shutting down of YGGDRASIL.
- Momonga modifies the setting of Albedo to be madly in love with him.
- Momonga is transformed into his game avatar.
- NPCs of the Great Tomb of Nazarick begin to have sentience.
- Momonga orders Sebas to survey the outside surrounding of Nazarick while the Pleiades guard the 9th Floor to prepare for any intruders.
- Momonga orders Albedo to assemble the Floor Guardians at the Amphitheater of the 6th Floor with the exception of Gargantua and Victim.
- Momonga tests the Staff of Ainz Ooal Gown.
- Aura and Mare battle against the Primal Fire Elemental for exercise.
- Floor Guardians assemble and pledge their absolute loyalty to Momonga.