There has been several Nonary Games in the Zero Escape universe, though they all share the same basic characteristic: the vital importance of the number 9. All the participants wear a bracelet/watch with a number on it, and which also guarantees that they follow the rules of the game. Otherwise, the watch either explodes (999) or injects them with a deadly mix of an anaesthetic and a muscle relaxant.
The first two Nonary Games revolve around the concept of digital roots: the ships in which they take place have several locked doors with numbers written on them. These numbered doors are only accessible by the three participants whose bracelets amount to the number written on the door after combining them to a single digit. This way, if Junpei (watch nº5), Santa (watch nº3) and Seven (watch nº7) team up, they will be able to access door number 6, since: 5+3+7=15, 1+5=6.
The third Nonary game operates under similar principles, but instead of several numbered doors, there is only one door, appropriately numbered with a big red 9. The most important novelty is the introduction of a second section to the game: the AB Game: the number 9 door will only open for those who have 9 or more points in their watch, and those points are gained after each round of room escaping is completed.
In order to open it and escape, the participants of the game have to, once again, form teams of 3 (2 pairs and a solo) based on the colors assigned to their watches and those of the three doors they have to go through. Once they have escaped from the locked room and return to the main warehouse, they are forced to play the AB Game: the pair plays against the solo they teamed up with, deciding whether they will Ally or Betray them. The solo, in another room, has to decide the same. If both Ally, each participant gets +2 points. If they Betray each other, they get 0 points each. But if one part Betrays while the other Allies, the betrayers will get +3 points, while the betrayed's total will be reduced by 2 points. After the AB Game is done, the colors of the watches are shuffled and a new round begins.
The Nonary Games
The First Nonary Game
The first Nonary game took place before (and, in a way, concurrently to) the events of Nine Hours, Nine Persons, Nine Doors. Among its participants were Akane (aka June), Santa, Clover and Snake. The first Nonary Game was organized by Ace (aka Gentarou Hongou, the CEO of Cradle Pharmaceutical) as a way to research the nature and potential use of the morphogenetic field.
The Second Nonary Game
The bulk of 999 takes place during the second Nonary Game, in the Nevada facility. It is revealed later in the game that this installment of the Nonary Game was organized by June, posing as Zero, and her brother Santa. The sole aim of this Nonary Game was to allow young June, trapped in the final puzzle of the first Nonary Game, to peek at different possible futures and save herself from being incinerated. She accessed the morphogenetic field and, with Junpei's help, she escaped from the incinerator.
The Third Nonary Game
The third and, for the moment, last Nonary Game is featured in 999's sequel, Virtue's Last Reward. This instance of the game was organized, again, by Akane Kurashiki (aka June), now an old woman, and Zero Sr. Though the protagonist of Virtue's Last Reward, Sigma, was kidnapped on December 25th, 2028, this Nonary Game takes place 45 years in the future. Zero Sr. is revealed to be old Sigma himself and the whole Nonary Game a way to send his consciousness back to the past in order to prevent the spreading of Radical-6 and the subsequent explosion of several "annhihilation reactors", which almost destroyed the Earth.
At the conclusion of the game, the consciousness of young Sigma (who had been inhabiting his older body) is sent back in time, a few days after he had been captured. In other words, right after he had attempted to contain Radical-6 for the first time (and lost both arms and his right eye in the process). He is greated by a young June, who informs him that he will have to spend the next 45 years reliving his future life and preparing for the inevitable third Nonary Game. Nevertheless, this time things will be different, as his mind will be fully accustomed to jumping from one parallel history to another, and so he will be able to go back in time to and finally stop Radical-6 from being released. How he will accomplish such a feat is still to be seen.