Awakened

Berserk Mode is an unofficial term used to refer to the state of mind that Yuya and his counterparts occasionally enter. Series director Katsumi Ono has referrred to it as Awakened or Enlightened (覚醒 Kakusei) in Japanese interviews. The ability changes the user's personality, voice, and mannerism to a more malevolent one and causes their eyes to glow.

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. It is also possible to force the activation of the ability by forcefully amplifying the aggressiveness of the user through electrical shocks. The activation of Yuya's Berserk Mode is depicted by the opening of an eye, followed by the instant annihilation of a shadowed city.

While Yuya and his counterparts 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 merged with one of their counterparts, they become vulnerable to being influenced by that counterpart's own memories and desires.

Each counterpart's eyes glow a different color when berserk: Yuto's eyes glow blue, Yugo's green, Yuya's red, and Yuri's purple. Of the four, Yuya's eyes are the most distinct, as only his iris and pupils glow in contrast to his counterparts, and the glow becomes stronger the longer he remains in Berserk Mode. There are currently four stages to Yuya's Berserk Mode, with each stage capable of progressing into the next with enough time.

In Stage I, his irises glow but Yuya remains in control. He is shown to enter this stage while Xyz Summoning Odd-Eyes Rebellion Dragon with a conscious mind.

In Stage II, Yuya becomes collected and cold, speaking no more than necessary. Additionally, his hair becomes wild and his voice deeper (his voice remains the same pitch in the dub, though it becomes rougher), both his iris and pupils glow and mute any natural shine to them. He is occasionally surrounded by a dark aura.

In Stage III, Yuya's hair sticks upwards, his pupils glow white, and he is constantly surrounded by a dark aura. He also becomes vicious and even sadistic, shown by his ruthlessness while Dueling the Obelisk Force and continued to thrash about while restrained by his friends. He is also capable of unleashing powerful shockwaves that are beyond normal for a person originating from the Standard Dimension.

In Stage IV, Yuya's pupils will glow even brighter and all of his counterparts will gain the same dark aura around them if they are in sync with Yuya. Yuya's anger in this stage grows to an almost primal rage, he become impervious to reason. This stage takes such a toll on their minds that all of them pass out afterwards, their eyes becoming dull and empty as the glow fades.

After consciously learning of his Berserk Mode, Yuya has become capable of breaking out of it by sheer force of will. However, with each stage of Berserk Mode that Yuya progresses through, it becomes increasingly harder to break out of it, with Stage IV making it impossible for him to quell himself.

Jean-Michel Roger is somewhat aware of Berserk Mode, as he intensified the power of the chip he implanted in Yuya's helmet to awaken the ability.

It also seems that when all four of Yuya and his counterparts are in the same place at the same time in Berserk Mode, they tend to claim uniting into one, as well as causing a distortion in the sky.

Pre-Arc League Championship
The very first instance of Berserk Mode occurred in Yuya's Duel against The Sledgehammer, during which Yuya achieved 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 did not glow and the only change was him becoming more confident and serious, lacking any rage-filled desire to annihilate his opponent.

Arc League Championship
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, who remained gripped by the state until after his victory and didn't quite remember what he'd done.

Later in his Duel against Iggy Arlo, 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 Iggy.

During his Duel against Taka and Nagi, "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 Knights of the Duel Disks 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 remained berserk and continued to where Sora and Shay were dueling, but was restrained by Gong, Aura, Reed, and Trout. While restrained, Yuya only kept on yelling violently in pain and struggling to escape (biting and uppercutting Trout) until passing out. Aura was able to determine that there were two souls 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. After resting, Yuya returned to normal and was consciously informed of this state, along with what he'd been doing while berserk and what Aura had discovered.

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.

Friendship Cup
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.

During the rematch between Dennis and Shay, Yuya briefly entered Berserk Mode again after learning about the former's affiliation with Duel Academy, but he managed to control his anger and snapped out of it.

Friendship Cup Finals
When the chip Roger planted inside Yuya's helmet activated during Yuya's Duel with Crow Hogan, Yuto, Yugo, and Yuri synchronized with Yuya's pain and all four went berserk. When Yuya Summoned "Odd-Eyes Rebellion Dragon", his eyes glowed brighter while Yugo and Yuri started to gain dark auras around themselves. When Yuya won the Duel, all of them passed out and the chip was destroyed in the process.

The state was invoked again when Yuri, the Obelisk Force, and Yugo arrived at Yuya's location. With Yuya controlling "Odd-Eyes Pendulum Dragon" and "Dark Rebellion Xyz Dragon" in his Duel with Barrett and Yugo and Yuri summoning their "Clear Wing" and "Starve Venom Fusion Dragon" respectively, all of the Four Dimension Dragons were in play at the same time, causing Yuya and his counterparts to enter Berserk Mode and synchronize again. After entering both states, Yuya, Yuto, Yugo, and Yuri started shouting that they waited for this time to become one and for a revival. But, before the distortion caused by their dragons finished Zuzu arrived and her bracelet teleported Yugo and Yuri away while Yuto's consciousness sank away.