Awakened

Berserk Mode is an unofficial term used to refer to the state of mind that Yuya, Yuto, and Yugo occasionally enter.

Effects
This ability causes Yuya and his dimensional counterparts to go into a state of rage, and their eyes to glow. This usually occurs in a Duel invoking the Four Dimension Dragons where the dragons overtake their owner's mind, or when the user is sufficiently angered, and its activation is usually accompanied by an excruciating amount of pain. While they are in Berserk Mode, they are willing to harm or destroy their opponent in order to win the Duel. When they regain their senses, they generally have no knowledge of what happened while they were in Berserk Mode unless prompted. If they enter Berserk Mode while being merged by one of their counterparts, they become vulnerable to being influenced counterpart's own memories and desires.

Notably, Yuya's Berserk Mode is slightly different from Yuto and Yugo's. Instead of going into a blind, homicidal rage, Yuya becomes colder and drastically more serious. In this state Yuya concentration peaks and he focuses completely on the duel, blocking out all sounds with the exception of his opponent's voice. His eyes also do not glow in the same manner as Yuto and Yugo's when they are berserk.

There are currently three stages to Yuya's Berserk Mode. In the first stage, his irises glow but Yuya remains in control. In the second stage, Yuya becomes collected and cold, speaking no more than necessary. Additionally, his hair becomes wild and his voice deeper, both his iris and pupils glow red, and he is occasionally surrounded by a dark aura. However during his Duel against the Obelisk Force, Yuya instead acted on Yuto's deep hatred for the Fusion Dimension for invading the Xyz Dimension and proceeded to defeat them ruthlessly. In the third stage, Yuya's hair sticks upwards, his pupils glow white, and he is constantly surrounded by a dark aura. He is also capable of unleashing powerful shockwaves that are beyond normal for a person originating from the Standard Dimension. Once aware of the circumstances, however, Yuya has become capable of breaking out of this mode by sheer force of will.

Because he absorbed and merged with Yuto's soul, Yuto can indirectly take control of Yuya, although both souls become increasingly vulnerable to an unknown darkness.

Each counterpart's eyes glow a different color when berserk: Yuto's eyes glow blue, Yugo's green, and Yuya's red.

History
The very first instance of Berserk Mode occurred in Yuya's duel against The Sledgehammer, which allowed Yuya to perform Pendulum Summoning for the first time. After the duel concluded, Yuya snapped out of that state and did not remember what he did. Unlike the other instances of Berserk Mode, Yuya's eyes do not glow and the only change was him becoming more confident and serious as well as lacking the rage-filled desire to annihilate his opponents.

Berserk Mode was properly introduced during the Duel between Yuto and Yugo. When Yuto Xyz Summoned his "Dark Rebellion Xyz Dragon" and Yugo Synchro Summoned his "Clear Wing Synchro Dragon" their eyes glowed. After being reminded by Yuya that he didn't want to hurt anyone, Yuto came out of Berserk Mode but lost to Yugo a moment later.

Later in his Duel against Isao Kachidoki, Yuto appeared in Yuya's mind and the two merged, causing Yuya to enter Berserk Mode and use Yuto's "Dark Rebellion Xyz Dragon" to win the Duel. When Yuya regained his senses, he was met with concerned stares from the audience and disdain from Isao.

During his Duel against Makoto Takeda and Ken Umesugi, "Dark Rebellion" appeared in Yuya's mind and he would have entered Berserk Mode had his ally, Dennis Macfield, not managed to bring him back to his senses before it fully consumed him. Though Yuya did summon "Dark Rebellion", he was able to remain in control for the remainder of the Duel.

After seeing the Knight of Duels students being turned into cards by the Obelisk Force, Yuto's memories of when Heartland was invaded and his vengeful hatred towards the Fusion Dimension flooded into Yuya's mind, triggering Yuya to enter Berserk Mode again to take revenge on them. This time, Yuya's Berserk Mode took on a whole different level; Yuya became more brutal and even enjoyed inflicting damage to his opponents. During the Duel against the Obelisk Force, Yuya progressively became more malicious and violent, becoming surrounded by a dark aura, and ultimately he summoned "Odd-Eyes Rebellion Dragon" to defeat them all at once. After winning the Duel, he continued to his next target, Sora Shiun'in but was restrained by Gong, Mieru Hochun, Michio Mokota, and Teppei Tairyobata. Yuya only kept on yelling violently in pain until he snapped out of Berserk Mode. Mieru was able to determine that there were two hearts within Yuya, along with a terrifying darkness. Yuto's soul was the one who initially triggered the Berserk Mode, but the darkness eventually took over both souls and caused their anger to intensify.

When Yuya saw his friends being sealed into cards by the Obelisk Force, he briefly entered Berserk Mode once more and chased after Sora. After reaching Sora, Yuya recalled Yuto's words and managed to calm down.

Goaded by Declan in their Duel, Yuya was about to enter Berserk Mode again before snapping out of it on his own. He briefly entered Berserk Mode again during his Duel against Duel Chaser 227, and though he snapped out of it soon enough, Yuya retained the serious demeanor throughout the rest of the Duel.