Interdimensional War

The Interdimensional War is an ongoing conflict between Astral World and Barian World, with Earth caught right in the middle. It ultimately serves as the main plot point of Yu-Gi-Oh! ZEXAL. The Numeron Code is the ultimate goal of both sides as it decides the victor and fate of both worlds and Earth.

Beginnings and Past Lives
Astral vs Don Thousand

It is said that the emissary of Astral world: Astral fought against the god of the Barian World: Don Thousand. Astral ultimately emerged victorious, sealing Don in the Sea of Ill Intent, but brought chaos to the Earth in the process.

Past Lives

It is revealed that before becoming Barians, the Seven Barian Emperors were human once in their past lives, with each of their past being connected to each ruin the Legendary Numbers were hidden in, along with the numbers themselves and their protectors.

Prelude

Not much is known on how the war between the two dimensions really started, with the only clue being said from Durbe and Mizael that one cannot exist while the other survives.

Barian World
Due to the fact that the residents of the Barian and Astral Worlds are high-energy beings that cannot interact with each other and being unable to take the Number themselves, Barian Emperors Durbe and Vector enlisted humans to do it for them, serving as their benefactors.

Dr. Faker
Faker was forced than recruited, as Vector threatened to hurt his child, Hart, unless Faker brought Vector "Numbers", which would appease him.

Hart Tenjo
Like his Father, Hart became a forced pawn of Vector from receiving his Barian energy, which not only gave him powers, but a few harmful side effects as well. From this he would be forced to use his powers to aid Faker in destroying the Astral World.

Vetrix Family
While Vetrix wandered the Barian world, Vector freed him and sent him back on Earth. Vetrix, thankful of this act, aided Vector and was tasked to bring the "Numbers" and Vector gave him and his sons power in the form of crests, though Vetrix only wanted one thing - revenge on Dr. Faker.

Astral World
The Astral World, through the Barians' recruitment process and Dr. Faker's offering, would gain the assistance of two beings who believe in possibilities and posses incredible tenacity: the great adventurer Kazuma Tsukumo and by extension his youngest child, Yuma Tsukumo.

Kazuma Tsukumo
Kazuma found the Astral World for a short moment before going back to Earth with a golden relic given to him by someone looked like Astral or Astral himself, which he gave to Yuma. He and his wife began to believe that through dueling, Yuma would eventually have to bear a great and dangerous destiny. Thanks to Dr. Faker's betrayal, Kazuma was sent into Astral World again and was trapped within it. From here, he sent Astral to Earth to help Yuma.

Yuma Tsukumo
Since receiving the golden key, Yuma began to dream about a door. One day, during a duel with Shark, Yuma unlocked the Door, which led to meeting Astral, with the unintended effect of having his memories scattered into 99 "Number" cards. By teaming up with Astral, Yuma hunts down the "Numbers" through many trials and adversity, ultimately becoming a key player in the fight against the Barians.

Three-way Rivalry Battle for the Golden Key that can unlock new possibilities
Yuma is surprised by being told of a ship within his key by Astral. Astral also states that only by gathering the "Numbers" will they solve its mysteries.

Meanwhile, Kite began to grow more concerned for Hart as his physical and mental well-being continued to worsened from using his powers, but Hart insisted on continuing since he believed he was helping the world, while Mr.Heartland told Kite to focus on gathering "Numbers" if Hart is to be healed. Kite suspected that Dr.Faker was hiding the truth behind the mystery of the "Numbers", so he had Orbital 7 research their origins, which lead to Kite seeking the Emperor's Key Yuma wears which their connected to.

WDC: Battle of the Human Recruits
In a effort to help Kite Tenjo gather "Numbers" more quickly, Dr. Faker and Mr. Heartland devised a very clever plan: Holding a Duel Tournament called the World Duel Carnival. Duelists from all over the World will come to Heartland City to wage heated duels, all to claim the Title "Duel Champion". During the tournament, Yuma and Astral faced off against not only Kite and Shark but other strong duelists as well, Number holders or otherwise, including those of a more mysterious, powerful and sinister group known as the Vetrix Family.

Attack of the Barians
Due to Vector's failures with his pawns, the Seven Barian Emperors decides to take more direct action in gaining the numbers and dealing with the users of Zexal.