Five years before the WDC, Kazuma, Dr. Faker and Byron Arclight went on an exploration to find the door to parallel worlds. Dr. Faker betrayed his companions and used them as sacrifices to open the door. As a result, the two of them were sent to alternate dimensions: Kazuma ended up in Astral World, while Byron ended up in Barian World.
Dr. Faker later made a pact with a being from Barian World that if he destroys Astral World, he would obtain the power to conquer the Earth. Therefore, he used Hart Tenjo's powers to transport large amounts of trash through a small hole in space into Astral World, where they would detonate. However, this is revealed to be fraudulent and Faker had really made the deal in order to cure Hart's illness and the destruction of Astral World was the price the Barian demanded for his services.
Following these attacks, Astral was sent to Yuma Tsukumo's world with a certain mission. Astral conjectured this was Kazuma's plan to defeat Byron, now Vetrix, and Dr. Faker's machinations. However, Vetrix speculated that Kazuma had sent Astral as his own instrument of revenge against Faker. In truth, Astral was sent in order to retrieve the Numeron Code, an all-power card that can shape reality before the Barians are able to find it, with which he must use to annihilate Barian World. and therefore allow Astral World to "Rank-up" to a higher realm of existence.
It is first seen when Astral obtains his third memory as as result of acquiring "Number 34: Terror-Byte". Astral had not previously remembered where he came from. Astral later recalls Astral World under attack, being assaulted by numerous explosions as its unseen denizens scream.
Astral World has a counterpart called Barian World. Kite Tenjo correctly guessed that using a stone from that world found inside Orbital 7 would open the Emperor's Key, which comes from Astral World, and he mentioned the world itself when Astral questioned him about why he hunts the "Numbers". Later during their Duel, Astral said a legendary power called ZEXAL can save his world.
Astral World and another world sent a wave of energy that collided with the Human World, causing time to temporarily stop and a sun from each world to appear. Dr. Faker explained that it is because the worlds are getting closer. Dr. Faker also said that something bad will happen soon because of this.
When Vetrix began the ritual to steal Hart's powers, the former was able to briefly see Astral World while taking more power from the latter. The Vetrix Family as a whole seems to be familiar with Astral World as well, as Trey recognized Astral as a being from that world when he briefly saw him. After Number 96 mastered the power of Chaos, he opens a portal to this world and Barian World, then he launches powerful attacks into both worlds and there were screams from the denizens of this world.
Mentioned by Eliphas, everything is capable of Shining Draw in this world and explained that it is the true Dueling style of his world. He told Yuma that Astral's mission was to destroy Barian World, which Astral has not accomplished and instead he became attacked and possessed by the power of Chaos. Eliphas told Yuma that his partnership with Astral caused the problem. However, when Yuma was able to defeat Eliphas in a Duel, he and the citizens of Astral World became convinced of a new possibility for the future and that abandoning Chaos was a mistake, thereby allowing Yuma and a newly-revived Astral to end the war with Barian World as they saw fit.
After defeating Don Thousand, Astral later used the Numeron Code to reunite the high-energy dimensions into a single parallel world. Eliphas mentioned this also allowed Chaos to return, causing upcoming challenges to take place.
Dr. Faker and Mr. Heartland's goal is to destroy Astral World, because they claim that it is evil, and that otherwise our planet will be destroyed. They also refer to Astral as Astral World's messenger, who should be destroyed as well. According to Dr. Faker, Haruto Tenjo has a hidden power that allows him to communicate with the spirits of Astral World. It seems that Haruto can also create powerful attacks, like a huge fireball, and send them directly to it through a portal. When Astral absorbs "No. 22: Zombiestein", he recovers the memory of Astral World being under attack.
Luna tells Shark that Dr. Faker must be stopped. Also, after absorbing three consecutive "Numbers", Astral explains he recovered some memories: his enemy is Dr. Faker, who plans on using the hidden powers of the "Numbers" to destroy Astral World; However, it is linked to this world. So, if Astral World is destroyed, this one will be destroyed as well. The Numbers Club then decide to save the world from Dr. Faker.
In a flashback, Kazuma Tsukumo is shown telling Akari Tsukumo that he discovered Astral World. He explains that that's where Duel Monsters are from, and that supposedly, the souls of the people there exist in a higher plane than ours. Some time later, Kazuma and Mirai disappeared in Astral World. Kazuma appears to Akari as a spirit revealing that he found a way in to Astral World. He tells Akari that this world would soon suffer a great disaster and that Yuma would be the one to open a new path to save it, and gives Akari the Emperor's Key to give Yuma.
Like Astral, the residents of Astral World, minus Kazuma Tsukumo and Mira Tsukumo, have varying shades of blue skin. They were injured by the attacks launched by Hart Tenjo and Number 96, causing them to suffer injuries such as cracking faces. Yuma was able to cure them with the power of Chaos.
Just like its counterpart, Astral World and Earth are connected. When humans die, it is possible for them to be reincarnated in Astral World if their hearts are noble and pure.
Due to Astral World's desire to Rank-Up, any soul who possesses the power of Chaos, was banished from this world, leading to the creation of Barian World. To further its desire to Rank-Up, the Astral World sought to destroy Barian World through Astral, but through Kazuma and Yuma's efforts, the world began to consider abandoning the power of Chaos an error. This mistake is resolved once a changed Astral used the Numeron Code to fuse the two worlds back together, which brought up many new challenges for the world in the process.
Unknowingly, through Astral bonding with his missing other half, Yuma managed to convinced Eliphas of their world's folly of banishing Chaos-wielding souls from Astral World and trying to destroy Barian World.