Dimensional Counterparts

A dimensional counterpart (似た者同士 Nitamono dōshi, lit. Fellow look-alike) is a phenomenon featured in the Yu-Gi-Oh! ARC-V anime, in which a person from one dimension resembles another person from another dimension. In addition to sharing the same face, the counterparts seem to be drawn to each other for an unknown reason.

History
Accordingly to Reo Akaba's actions, it is hinted that these counterparts, the girls in particular, are important to his plans. For this purpose, he locked up Serena inside the Academia Castle for most of her life and ordered Yūri to bring the other remaining girls, Ruri, Rin, and Yuzu. Each of this girls bears uncanny resemblance with each other and possesses a bracelet with special powers that is connected to the boy dimensional counterparts, Yūya, Yūto, Yūgo, and Yūri.

Mistaken Identities
A common recurrence is for a character to confuse one counterpart with another counterpart due to their identical facial structures. Instances of confusion include:

Yūya Sakaki
Yūya was the first character to have a dimensional counterpart. Each of these counterparts has a Dimensional Dragon and also can enter a rampant state of mind, which has been given the title "The Awakening" by the animation staff or "Berserk Mode" by fans. They are also able to sync their mind with each other as well. When the they summoned their dragons at the same place and time, they will automatically enter their rampant state of mind and synchronised with each other that will open a dimensional hole in the sky. These dimensional counterparts seems to be originally a single being, as the moment the dimensional hole appears, they will try to reach the hole as they stated that they "have been waiting for the moment of their revival and become one".

Yuzu Hīragi
The second character to be known to have dimensional counterparts was Yuzu. Similarly to Yūya and his counterparts having Dimensional Dragons to help signify themselves as counterparts, Yuzu and her counterparts wear unique jeweled bracelets, which have mysterious abilities. For this reason, they are collectively called Bracelet Girls (ブレスレットの Buresuretto no Ko).