Astral World

The Astral World (アストラル世界 Asutoraru Sekai) is the dimension where Astral was born and a location in Yu-Gi-Oh! ZEXAL series. According to Astral, only individuals who have Ranked Up in a spiritual way can reach this world.

Structure
The Astral World is a world made of various powerful energies and is colored light blue.

Etymology
Astral means "of the stars" and is also used to described things relating to a nonphysical realm of existence. The Astral World is referred to as the "アストラル世界" (Asutoraru Sekai). Sekai more generally means the World proper, and/or the Universe.

History
When Kazuma Tsukumo fell from a cliff in a snowy mountain during one of his explorations with his wife, he landed in the Astral World, and obtained the Emperor's Key. It is unknown if that was just his spirit as his body was severely damaged when he woke up, though Astral has stated that only those with "ranked-up souls" may enter the Astral World, which may be obtained by working towards one's greatest goals.

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 the Astral World, while Byron ended up in the Barian World. Dr. Faker later made a pact with a being from the Barian World that if he destroys the 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 the 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 the 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 find it.

Yu-Gi-Oh! ZEXAL
It is first seen when Astral obtains a memory as as result of acquiring "Number 34: Terror-Byte". Astral had not previously remembered where he came from. Astral later recalls the Astral World under attack, being assaulted by numerous explosions as its unseen denizens scream.

The Astral World has a counterpart called the 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 the 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.

The Astral World and another world sent a wave of energy that collided with the world where Yuma Tsukumo and Astral currently are, 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 take Hart's powers, the former was able to briefly see the Astral World while taking more power from the latter.

The Vetrix Family as a whole seems to be familiar with the Astral World as well, as Trey recognized Astral as a being from that world when he briefly saw him.

Manga
In the manga, Dr. Faker and Mr. Heartland's goal is to destroy the Astral World, because they claim that it is evil, and that otherwise our planet will be destroyed. They also refer to Astral as the 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 the 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 "Number 22: Zombiestein", he recovers the memory of the 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 the Astral World; However, it is linked to this world. So, if the Astral World dies, this one will die as well. The Numbers Club then decide to save the world from Dr. Faker.