Academia

 Academia' (アカデミア Akademia) is a mysterious school in the Yu-Gi-Oh! ARC-V'' anime that trains "Duel Soldiers" and is located in the Fusion Dimension. It is an alternate universe version of Duel Academy from the ''Yu-Gi-Oh! GX'' anime. It is run by Reo Akaba under the guise of "The Professor", a man originally from the Standard Dimension, and serves as his base of operations.''' The goal of Reo Akaba and as such the goal of the Academia, is to use the power of Fusion to make all the worlds become one. In order to accomplish this, the Academia employs its army of Duel Soldiers in order to conquer the other Dimensions by turning its inhabitants into cards.

Strategies
In Episode 40, Serena mentioned that Barrett is using a "By-The-Books" strategy, a kind of strategy used by the Academia.

History
Three years in the past of the ARC-V storyline, Reiji Akaba had unknowingly traveled to the Academy via an interdimensional transporter. He eventually met Serena, who he helped escape from faculty members who were pursuing her, only to have them both caught by Reo and several members of Obelisk Force, the elite vanguard squad. Reiji was confused by the ensuing discussion about alternate dimensions and the Academia, until the squad hauled Serena off and placed a device on Reiji's wrist, which sent him back to Standard.

During his Duel with Shingo, Yūto asked about the connection between Leo Duel School and the Academia. However, Yūto soon discovered that most of LDS knew nothing.

After Shun Dueled Sora, it is implied that the latter was affiliated with the Academia, as Reiji mentioned they could learn more about it from Sora. During his Duel against Yūya, Yūto revealed that the Academia attacked the citizens of Heartland and sealed them in cards. During this time Sora was transported back to the Academia due to a program on his Duel Disk that activated after revealing his goal of acquiring a powerful Fusion Monster. When Sora came back Reo had his men check Sora's memories as to find out why Sora had been returned since Standard were not their enemies. During this time Reo noticed Yuzu whom he called the "Fourth Piece" he needed and ordered Yūri to bring her to him.

While Sora was recovering in the nursery he protested to go back to Standard since there were Xyz Remnants there, Serena eavesdropped on his demands and planned to go to Standard as to prove her strength to Reo in order to be at the frontlines. Several guards attempted to stop her but failed, but Barrett decided to go with her instead of stopping her since it was his duty to protect her. The two arrive at Standard and Serena watches Hokuto perform an Xyz Summon on screen, believing him to be part of the Xyz Remnants, she manages to find him and easily defeats and transforms him into a card. Serena then turns his attention into Yū Sakuragi a prominent Xyz User, in the Maiami Championship. Unfortunately for her, Reiji found about her appearance and correctly deduced she would attack Yū, so he used him as bait to lure the duo.

Serena and Barrett encountered Yū, but before they could attack him, Reiji appeared and ordered Yū to leave, while having Nakajima seal the area so the Academia Duo could not escape. Serena attempted to Duel Reiji but Barrett offered to Duel instead, since it was his duty to protect her. Serena stood aside and watched. Barrett and Reiji Dueled, with Reiji noticing that Barrett was a war veteran, as Barrett used burn tactics to rapidly damage Reiji. Barrett praised Reiji for using his own Life Points to maintain the cost of his "Covenant" cards, mentioning that he deserved a war medal for that. Reiji defeated Barrett using a combination of "DDD Marksman King Tell" and "DDD Oracle King d'Arc". Serena attempted to leave, but Reiji stopped her and the two reminisced on their past encounter years ago. A barely conscious Barrett activated his Duel Disk to return to the Fusion Dimension and to give away Serena's location. Reiji offered Serena the chance to join him into defeating Reo, but Serena refused, saying that all she wanted was to earn Reo's recognition. She left, but not before Reiji declared her an enemy should she interfere with him.

After receiving the transmission, Reo had a meeting with Sora, who requested to be sent back to the Standard Dimension. Reo agreed to Sora's request, but ordered him to look for Serena and make it his priority to bring her back. Sora noted Serena's resemblance to Yuzu and asked why the two looked alike. Reo replied that he did not need to know that and had the Obelisk Force accompany Sora. The Obelisk Force entered the Standard Dimension during the Maiami Championship's Battle Royal, prompting Reiji to cut any transmission that featured the Academia. Sora encountered Shun, Yūya and Knight of Duels students. Sora had the Obelisk Force deal with the Knights while he Duels Shun on nearby ruins. The Knights of Duels were then swiftly defeated and sealed into cards. Seeing this, Yūya became infuriated and challenged the three soldiers to a Duel. Meanwhile, Reiji sent his Junior Force of Lancers, led by Yū.

While Yūya Dueled against the Obelisk Force "Dark Rebellion Xyz Dragon" to attack them. The trio of soldiers began to panic but they were unable to defeat Yūya, who used "Synthesis Magician" and "Antithesis Magician" to Pendulum Summon "Odd-Eyes Pendulum Dragon" and then used the Pendulum Effects of both his Pendulum Monsters to grant "Dark Rebellion" a Level equal to the Level of "Odd-Eyes". Yūya overlaid his two monsters to Xyz Summon "Odd-Eyes Rebellion Dragon the Supreme King Black Dragon" and used its effect to destroy their monsters, inflict effect damage and attack a number of times equal to the monsters destroyed. This defeated all three soldiers in one fell swoop.

More Obelisk Force soldiers entered the Volcano Area and spotted Serena with Dennis Macfield and Yuzu. They escaped, leaving Yū and the rest of the Youth Lancers to fend off the invaders. However the Youth force was quickly overwhelmed and turned into cards. Before Yū was defeated, Yūgo interfered in the Duel after recognizing the Academia soldiers as people he met before. He defeated the soldiers by using their "Antique Armageddon Gear" against them with a combination of his "Clear Wing Synchro Dragon" and "Synchro Cracker" to destroy all monsters with lower ATK than "Clear Wing". Yū realized that he could not fight any further and ran away in a panic without thanking Yūgo, annoying him. Nakajima expressed his concern to Reiji that the Youth Force were unable to repel the invaders and Reiji acknowledged the LDS did not have the strength to fight the Academia, but that his plan for the Lancers was for them to master Pendulum Summon as a new power that could give them an edge in battle. He referred to the potential Duelists as the "Yūya Sakaki Generation".

While the battles were taking place, Yuzu and Serena talked, and Serena revealed that the Academia, under orders of "The Professor", plotted to make the Four Dimensions become a single world, calling it an "honorable goal". However Yuzu revealed the truth of the Academia's cruel assaults into other dimensions to Serena and requested for her to seek the truth. Knowing that the Obelisk Force were hunting Serena down, Yuzu suggested they change clothes so that Serena could meet Shun and confirm the truth. Dennis, now revealed to be an agent working for the Academia, eavesdropped on their conversation and met Yūri, telling him of the girls' plan so that he could track Yuzu. During this time, Halil and Olga appeared, mistaking Yūri as an opponent for the Battle Royale, and challenged him to a Duel. Yūri was annoyed, but he accepted their challenge. He easily defeated both of them and sealed them into cards. The Obelisk Force surrounded Yuzu, believing her to be Serena, but Yūri interfered and ordered the soldiers to retreat or he would seal them into cards as well. He threw the cards containing Halil and Olga at them, causing the soldiers to leave. Yūri tried to convince Yuzu to surrender, claiming it was pointless to fight and that "the Professor" needed her. Yūri challenged Yuzu to a Duel, which Yuzu was forced to accept.

Yūya and Gongenzaka, who were looking for Yuzu, encountered Dennis and told him of the attacking soldiers, unaware of his true colors. Dennis maintained his facade by agreeing to accompany Yūya and Gongenzaka. Meanwhile, Yuzu was forced to run for her life after knowing that she was no match for Yūri, who was in hot pursuit with Dragon. Before Yūri could find her, Yuzu's bracelet activated teleporting Yūri away, due to Yūgo's arrival. Yūgo mistook her for Rin. Before Yūya could find her, the bracelet shone once more and teleported the two away leaving Yūya, Gongenzaka and Dennis unable to find her. Dennis incorrectly believed that Yūri had finished his mission.

Serena, who managed to avoid the Obelisk Force, witnessed Shun being defeated by Sora and thrown downstairs, leaving him injured. Serena activated "Lunar Eclipse" so that the two of them could escape. Sora initially mistook Serena for Yuzu and ordered her to stand aside. Upon recognizing her Duel Disk as being of Academia origin, Sora pursued the pair. The three eventually reached the Volcano Area with Sora requesting to get his "prey". However the two Fuma Ninja students, Tsukikage and Hikage appeared and blocked Sora's path. Hikage decided to face Sora, allowing Serena, Shun and Tsukikage to escape. Dennis, observing from afar, encountered remnants of the Obelisk Force. He told them that Serena was in disguise. The three soldiers asked Dennis if he wasn't coming, but Dennis said he couldn't because there were "too many cameras". The Obelisk Force soldiers then attacked Serena, Shun and Tsukikage, and forcing them into a Battle Royale. Shun wanted to go first, but Tsukikage interfered and fended off the attacks of the three soldiers using "Barrier Ninjitsu of Gathering Shadows". Serena decided to go next and Fusion Summoned "Moonlight Cat Dancer". Before it could attack, the Obelisk Force used "Fusion Dispersal" to counter her monster and damage her, as they prepared for her. Michio Mokota and Teppei Tairyōbata then joined the Duel, but suffered a 2000 LP penalty. Using a combination of "The Legendary Fisherman III" and "Monster Pie" the two were able to damage the entire Obelisk Force for 2000 LP each one. The Obelisk Force used a combination of "Antique Gear Reborn", "Antique Gear Spark Shot", "Antique Gear Booster" to deal enough damage to defeat Michio and Teppei, who were weakened by the penalty. Both were sealed into cards afterward. Before Tsukikage could suffer from the same fate, Shingo appeared and used "Flame Guard" to protect him, having heard the situation from Reiji, but took the 2000 LP penalty.

Yūya and Gongenzaka watched Sora seal Hikage into a card. Gongenzaka then saw Serena, who he mistook as Yuzu, in a Duel and left to help her. Yūya was left alone and challenged Sora to a Duel in order to return his smile. Sora agreed, since he did not like having a losing record against Yūya. Gongenzaka arrived as Shingo used "Abyss Actor - Devil Heel" and "Abyss Actor - Funky Comedian" to Pendulum Summon "Abyss Actor - Big Star" and used its effect to search and equip it with "Abyss Script - Fantasy Magic in order to return the Obelisk Force's "Antique Gear Triple Bite Hound Dog" to the Extra Deck and break their combo. However, the Obelisk Force used "Antique Gear Rebirth Fusion" to Fusion Summon "Antique Gear Ultimate Hound Dog" and used its effect to halve the Life Points of all their opponents. Gongenzaka took his turn, and used a combination of Pendulum Summon and the effects of two of his "Superheavy Samurai Thief" and a copy of "Superheavy Samurai Courier" in order to provide Shun with the Pendulum Cards that Shingo activated previously. Shingo questioned his move because he thought he could break the combination by himself, but Gongenzaka said it was fine this way. Shun asked why Gongenzaka went so far to give him Pendulum Cards. Gongenzaka replied that Shun was the one who would finish the Duel. During his turn, Shun remembered all the people who protected him during this time, and found the notion "laughable". Shun used "Devil Heel" and "Funky Comedian" to Pendulum Summon three copies of "Raid Raptors - Wild Vulture" and used them to Xyz Summon "Raid Raptors - Revolution Falcon". Shun used its effect to let it attack all the Obelisk Force's monsters. Its other effect allowed Shun to reduce their ATK and DEF 0 during battle. "Revolution Falcon" attacked and defeated the remaining Obelisk Force soldiers, winning the Duel for Shun and his allies.

Meanwhile Sora and Yūya perform their Duel with the two trading blows. Yūya was convinced that Sora had become warped and revealed his intentions to bring him back to his "usual self", but Sora refuted this by saying that the Sora that Yūya knew was never his true self; his true self was a soldier of Academia. Yūya disagreed because he remembered that Sora had fun during their first Duel. Sora retorted that he was not being serious back then, but Yūya claimed his smile was genuine and that the two became friends after that Duel. Sora told Yūya that there were things more important than friendship. Yūya denied this by pointing out that Sora taught Yuzu how to Fusion Summon as a sign of friendship, but Sora claimed he did so merely because Fusion Summon was an honorable mechanic and a power that could make the worlds become one. Yūya argued that fusing the four worlds was wrong, but Sora angrily stated the opposite. Yūya asked Sora if he was aware of the cruelty inflicted into the Xyz Dimension by the Academia, and Sora indifferently stated that it couldn't be helped to achieve the Academia's goals. An infuriated Yūya told Sora that they didn't have the authority to fuse the worlds.

Yūya Xyz Summoned "Dark Rebellion Xyz Dragon" and used its effect on Sora's "Death-Toy Scissors Tiger", but Sora used "Death-Toy March" in order to negate the effect and Fusion Summoned "Death-Toy Sabre Tiger", which subsequently revived the previously destroyed "Death-Toy Scissors Bear". The effects of both "Tiger" and "Sabre Tiger" boosted the ATK of Sora's monsters to colossal levels. Yūya then used "Synthesis Magician" and "Antithesis Magician" to Pendulum Summon "Odd-Eyes Pendulum Dragon". He used the effects of both Pendulum Monsters to make "Dark Rebellion" have the Level of "Odd-Eyes" and overlaid both of his Dragons to Xyz Summon "Odd-Eyes Rebellion Dragon the Supreme King Black Dragon" Yūya used its effect to destroy both "Tiger" and "Bear" since their Levels were lower than 7. Sora used "Fusion Front Base" to avoid the effect damage. At this point, Sora regained the same excited demeanor he had during his first Duel with Yūya because Yūya was able to Summon an Xyz Pendulum Monster, while finally realizing that battling Yūya is fun. Yūya agreed to his statement that Duels were meant to have fun. Yūya used the effect of "Rebellion Dragon" to attack as many times as monsters were destroyed by its effect. Sora activated "Flame Chain" to lower its ATK, but Yūya countered with "Flame Power" to boost its ATK. The two raced for an Action Card, but were unable to catch it since the Battle Royale timer expired, disabling the "Wonder Quartet" Field Magic and ending the Duel without a result. Gongenzaka and the others, who witnessed the Duel, caught up to Yūya. Yūya mistook Serena for Yuzu, and Serena revealed she was not Yuzu. Sora, knowing the mission had failed, activated his Duel Disk to be transported back to the Academia.

Technology
Their technology is advanced enough to create brain scanners that can access to one's memory. They are also shown to have interdimensional travel technology, as well as abilities to materialize Duels and technology to seal any human into cards.