Four Heavenly Dragons

The Four Heavenly Dragons (の Shiten no Ryū), also simply known as the Four Dragons (四体のドラゴン Yontai no Doragon) and referred as Four Dimension Dragons (４つののドラゴン Yottsu no Jigen no Doragon) by Zarc, are a series of Dragon-Type Monsters introduced in Yu-Gi-Oh! ARC-V. They are used by Yūya Sakaki and his dimensional counterparts.

History
These four dragons originally existed in the Original Dimension and once belonged to a Duelist named Zarc who was widely known for his ability to communicate with his monsters. He mostly used these four dragons to Duel. It's revealed by Leo's daughter, Ray, that the dragons, along with other monsters, possessed real souls. According to both Ray and Leo, the dragons were furious to be continuously used as tools for battle simply to satisfy the audience's desire and developed hatred for humanity. So when Zarc finally lost to his thirst for power and summoned them, the dragons, now having a physical body with mass due to the Real Solid Vision system, unleash their rage towards the people and began to destroy the world. Zarc, sensing the dragon were still not satisfied with their revenge and wished to destroy more like he did, used "Astrograph Magician" to fuse the five of them together, becoming "Supreme King Dragon Zarc" that eventually led the Original Dimension to the verge of destruction. They were stopped by Ray who used the four cards developed by Leo with natural energy, resulting the four dragons to be banished and split up again together with the Original Dimension. Since then, each of this dragon resided in their respective dimension and came into the possession of four boys who each has a fragment of Zarc's soul inside them.

Even after being separated, these dragons continues to be connected to one another as they resonate when they are in close proximity with each other, whether they are summoned during a Duel or not. When facing off against each other, their owners suffer an intense burning pain in their chest and may enter a Awakened state, dueling ferociously until their opponent is defeated  , although they are still capable of returning to their senses during the Duel. They can also cause their owners to synchronized with each other if they are in close proximity. Additionally, the dragons can influence their owners to summon them if the conditions for their summoning are met.

The Dragons are calling one another to become one again and to do so they are capable of traveling through dimensions, as Yūgo stated that he was guided to both the Xyz Dimension's Heartland City and the Standard Dimension by "Clear Wing Synchro Dragon". When one of them is defeated, its owner appears to be absorbed into one of their Dimensional counterparts. In Yūto's case, despite having lost to Yūgo, he was absorbed by Yūya who was closer to his position. However, ownership of the dragons seem to be determined by the dragons themselves, as Yūto only consented to give Yūya "Dark Rebellion Xyz Dragon" after said dragon conveyed something to him. When all four Dimension Dragons appear within close proximity at the same time, they will cause their masters to enter the awakening, synchronize, and attempt to combine with each other. This also caused a phenomenon of dimensional hole appear in the sky.

During the Lancers' battle against Academia, Zarc took control of Yūya and absorbed Yūri into him. Using "Astrograph Magician", Zarc once again fused the four dragons and revived himself as Supreme King Dragon Zarc. However, they were once again got split by Ray who was possessing Reira's body by using the En Cards. Due to Reira's quick action to seal Zarc into himself, Zarc was not split and instead revived as Yūya, resulting the four dragons to come into his possession. Yūya was initially afraid to summon the dragons out of fear it will awaken Zarc's soul inside Reira and bring harm to Ray and her incarnations, so he only summoned "Odd-Eyes Pendulum Dragon" in his matches until Yūto, Yūgo, and Yūri who were residing inside Yūya reminded him of Zarc's ability to communicate with monsters. Summoning the four dragons, Yūya sensed that the dragons' voices were not angry, but they were rather afraid of Ray after being split by her and that's why they wanted to prevent her revival. This made Yūya determined to prove to the dragons that they are already strong enough even without becoming Supreme King Dragon.

Each of the Dragons' names uses the following structure: "[Trait of the monster or the owner] + [Summon Mechanic Name] + Dragon". With the exception of the 2800 ATK "Starve Venom Fusion Dragon" they all have 2500 ATK and 2000 DEF (like most of the past protagonists' aces) and, in the anime, all of them have the common trait that their effects only affect Level 5 or higher monsters and are related to ATK. Their attack and effect names also follow similar patterns: the effect names are simply two English words, while their attack names follow the same pattern as previous Dragons, primarily the base "Eyes" Dragons; "[Japanese word] no [Two English words]."

In the Manga, the Dimension Dragons does not exist, but there are Manga counterpart.

Variations
Over the course of the series, Yūya and his dimensional counterparts receive newer forms of their Four Dimension Dragons by using them as Material for the three types of Extra Deck Summoning (Fusion, Synchro, and Xyz).

Trivia

 * Each of the four dragons has a unique trait that makes them different from the others:
 * Odd-Eyes Pendulum Dragon is the only Dragon that is ground type, incapable of flying.
 * Dark Rebellion Xyz Dragon is the only Dragon without level since it's a Xyz monster.
 * Clear Wing Synchro Dragon is the only Dragon with WIND Attribute, and do not have any orb-like object on its body nor legs.
 * Starve Venom Fusion Dragon is the only Dragon with 2800 ATK.
 * So far, Starve Venom Fusion Dragon is the only dragon whose attack and effect doesn't have any name. Nor it's last effect to be used.