Zarc

Zarc or Z-Arc (ズァーク, Zāku) is a character in Yu-Gi-Oh! ARC-V anime series. Before his revelation, he is known The Darkness or Black Shadow residing inside Yūya Sakaki and his dimensional counterparts whom he has a strong connection with.

Personality
Zarc used to be a normal Duelist who simply liked to Duel for fun. After the incident when his fans cheering for him after he accidentally injured his opponent, Zarc began to think that injuring his opponent in a Duel is a normal thing to do. Since then, he used more violent Dueling as his fans continue to jeering on him. However, as times went on, he developed violent impulses as he became frustrated that no one matched up to his strength while he wanted to become stronger. His thirst for strength eventually drove him mad, making him obsessed to become the strongest in the world by destroying everyone and everything in his way.

History
Zarc was a resident of the original dimension. He once was a Duelist who claimed able to hear the voices of the monsters and connected his heart with them. Due to this, he was very skilled in Duel and quickly gain advantage on field, soon becoming undefeated Duel champion and widely known as a superstar in Action Dueling. He started to change after his Duel style accidentally severely injured one of his opponents yet the audience kept cheering for him, leading Zarc to think it's fine even if his opponents are injured in the Duel. Since then, his Duel style became more violent, resulting his opponents sustained heavy injuries. At first, he simply wanted to answer his fans' expectations, however, as he continued to Duel more and more, Zarc became obsessed to become the strongest. Eventually, at the end of a tournament, he summoned his four dragons, "Odd-Eyes Dragon", "Dark Rebellion Xyz Dragon", "Clear Wing Synchro Dragon", and "Starve Venom Fusion Dragon" to destroy everything in his way. Feeling that his dragons were also not yet satisfied with their battles and seeks to attain the strongest power, Zarc fused himself with his four dragons using "Astrograph Magician", becoming a single giant dragon that people called as the "Supreme Dragon King Zarc". Despite the people's best efforts, they were all helpless against Zarc's overwhelming power and were annihilated without exception.undefined Zarc was on the verge to destroy the whole world until Ray opposed him with the four cards that Leo created, stopping Zarc's terror at the cost of the world to be splited into four dimensions. However, Zarc didn't completely perish, his soul somehow got split into four fragments residing inside four boys who shared the same face as him, Yūya Sakaki, Yūto, Yūgo, and Yūri.

Battle Royal
Zarc first appeared during Yūya's Duel with Isao Kachidokiundefined but was only recognized as a separate entity when Mieru Hōchun used her crystal ball on the out of control Awakened Yūya while he was restrained by Noboru Gongenzaka, Michio Mokota, and Teppei Tairyōbata. Through her crystal ball, it was shown that Zarc, only known as the Black Shadow or the Darkness slowly tried to overwhelm both Yūya and Yūto's souls while they were still in their Awakened state, though Yūya fell unconscious from his Awakened state before it could do so. Once Yūya regained his consciousness and realized his existence as well as Yūto's soul inside him, Yūya came to realization that Zarc was the one responsible for his violent Dueling against Isao and the Obelisk Force. This made Yūya scared for a moment, but he quickly dismissed it by remembering his father's encouraging words. Zarc resurfaced before Yūya's Duel with Sora after the latter sealed Hikage, though Yūto's spirit calmed him down by reminding him of their promise.

Friendship Cup Semi-Final
Zarc returned even stronger after Yūya was electrocuted by a chip in his helmet that increased his aggressiveness during his Duel with Crow. This caused him to awaken. Since both Yūgo and Yūri were also in vicinity, Yūya synced with them, forcing them to awaken with the same dark aura as him until he won the duel.undefined

Yūya vs. Barrett
When all four dimension dragons appeared during Yūya's duel with Barrett, Zarc returned and overwhelmed Yūya and his dragons, even giving the dragons a shadowy aura until Yuzu's bracelet ended the process by transporting Yūri and Yūgo along with their dragons.

Duel Against Edo Phoenix
While exploring Heartland Duel School, Yūya and Yūto discussed Zarc's strong control over them while they were awakened in their Duel against Barrett. Yūto recalled the Four Dimension Dragons' desire to become one and suspected that they have a strong connection to Zarc. He also theorized that his current residence in Yūya's body may have had to do with "Dark Rebellion's" will.

Duel Against the Tyler Sisters
During Yūya and Shun's Duel against Gloria and Grace Tyler, Yūya was worried about Yūto's anger controlling him because Zarc might return to possess them again.undefined

Yūri vs. Asuka
When Yūri confronted Yūshō and the others, Asuka Dueled him to buy some times for Yūshō, Reiji, and Reira to go on ahead so they can reach Leo. The Duel went to Yūri's favour, leading to his victory. Before he carded Asuka, Zarc made his appearance as purple aura that surrounded Yūri's body, though it's not visible to be seen. As if resonating with Yūri, he declared his goal that he will turn all people in all four dimensions into cards, which will prove himself that he is the strongest Duelist.undefined

Yūya and Yūto vs. Ruri and Serena
When a  Parasite Monster  tried to take over  Yūya 's mind, Zarc destroyed it, which caused Yūya to awaken briefly. Zarc returned when Yūya's anger caused him and Yūto to awaken after seeing  Yuzu  under the  Doctor 's control. Together, they Summoned " Odd-Eyes Raging Dragon " and defeated  Ruri  and  Serena, destroying the lab in the process. Zarc then disappeared after Yūya remained conscious. undefined

Yūgo vs. Yūri
When Leo finally met Reiji, Reira, and Yūshō at his throne room, he explained about the original dimension before it was split and how Zarc destroyed it. At the same time, Yūri and Yūgo finally confronted each other and started their Duel, summoning each of their respective dragons. The summonings of the two dragons caused all the pieces of Zarc's souls inside Yūgo, Yūri, Yūya, and Yūto to react stronger than usual even when Yūya nor Yūto have yet to summon their dragons. None of the counterparts were able to hold back Zarc's power, resulting Zarc to take over their bodies once more and declared to become one as a thunder shock suddenly bolted from the sky to between Yūri and Yūgo's field. Zarc's soul inside Yūya's body declared to use a card called "Astrography Magician" to become one, creating a strong blow of wind that enough to destroy the cage trapping them and blew away Kaito and Edo who came to help Yūya.undefined

Abilities
Zarc first awakened from inside Yūya when Yūto took over the former's body and initiated the Awakening, resulting Zarc to awaken inside Yūya as well. Zarc influenced Yūya and Yūto's Dueling style to become battle hardened and violent. Not only that, he also influenced Yūya's behavior, making him malicious with only desire to defeat his opponents and takes pleasure in causing and seeing harm to them, particularly Duelists from Academia due to Yūto's anger and hatred for them. Zarc also significantly strengthened Yūya's Awakening state more than usual that signed by a thick black aura surrounding Yūya's body. Consequently, while under his influence, neither Yūya nor Yūto are aware of their surrounding and if stopped by someone while not Dueling, Yūya became more unstable to the point of needing to be restrained until he finally reverted back to his normal self, usually falling unconscious.

When in a synchronized awakened state with all of his dimensional counterparts, they also gain dark auras around themselves as well until the synchronization ends. Zarc also protected Yūya from being taking over by Doctor's Parasite Monsters as they were quickly destroyed when they attempted to attach to his brain.