Overlord Prologue (1st Half) is a side story in the Overlord series. It was released on December 25, 2015, in Box 4 of the Blu-ray & DVD Collection.
The story starts before the guild Ainz Ooal Gown came into existence. It's about the clan Nine's Own Goal which Momonga was a part of. During their meeting, clan member Nishikienrai informs the other clan members that he has discovered an unexplored dungeon known as the Great Tomb of Nazarick. During the meeting, the clan leader, Touch Me, announces to the members he is dissolving the clan, and reforming them as a guild. A new name for the guild is decided and Momonga is recommended by Touch Me as their guild leader, which was accepted by all the members. As the guild leader, he announces that their first mission as a guild is to capture the dungeon in one try.
Suzuki Satoru returns home after another grueling day in the dystopic World of 2138. After eating a meal of multivitamins and liquid lunch, he retires to his chair and activates his Neural Nano-Interface. Through this device, he enters the DMMO-RPG game YGGDRASIL. Upon his entry into the game world, via a Waiting Area, Momonga is greeted by Peroroncino. Momonga notices his armor is different and asks how it came to be so. He realizes that Peroroncino used a Cash Item to enhance it, a direct violation of the No Cash Item Alliance creed. Momonga is disappointed in Peroroncino, but the later pleads it was the only way to enhance his armor. His pleas of forgiveness, however, make Momonga relents, admitting he likes the armor.
The two make their way to the meeting where the clan of Nine's Own Goal is taking place. At the meeting, Nishikienrai reports an amazing discovery, a new dungeon located in Helheim. The clan agrees to investigate the dungeon once the meeting is over. Immediately then after, Touch Me announces his intent to dissolve the clan, causing the rest of the clan to protest. Touch Me, however, informs them that he wishes to make Nine's Own Goal into an official guild, however, he does not wish to take over leadership of the guild and elects Momonga as its first guildmaster. No one complains, satisfied with the decision.
The next topic begins with the name of their guild, as it was decided that Nine's Own Goal could not be used. Warrior Takemikazuchi, however, changes the words of the original name and presents it as Ainz's Own Goal. The name is quickly accepted by the newly formed guild. At the end of the meeting, the guild departs to the location of the newly discovered dungeon.
- Information concerning the Neural Nano-Interface is only discovered here in this special.