Ouroboros (ウロボロス) is one of the Twenty World Items of YGGDRASIL.
In the past, Ainz Ooal Gown had laid claim to the Seven Hidden Mines. To prevent Ainz Ooal Gown from creating a monopoly on the rare metals within the mine, an enemy guild used the World Item known as Ouroboros to remove their presence from the World itself for at least a month. Once the duration effect of Ouroboros expire after one month then, Ainz Ooal Gown reenters it and realizes that the enemy guild have already seized the valuable metals in those mines.
The World Item is said to be a ring.
This World Item ability is a superior version of the Super-Tier Magic, "Wish Upon A Star" in that it can directly contact the operating company and ask them anything. In the past, a guild used it and requested the isolation of a certain world, preventing all players but their guild from entering for a month. In other words, it erected some sort of unknown seal around the world that stops players from gaining access to it. However, only those who possess a World Item are immune to its restrictions.
- The name Ouroboros refers to an ancient symbol depicting a serpent or dragon eating its own tail, which represents cyclicality.