Invasion of Xyz Dimension

The invasion of the Xyz Dimension was an event in the Yu-Gi-Oh! ARC-V anime.

History
Leo Akaba, the Professor of Academia, ordered his elite vanguard squad to advance into the Xyz Dimension and attack, as part of his plan to eventually unite the Four Dimensions. Dennis Macfield was sent to the Xyz Dimension to find one of its people, Ruri Kurosaki, and green-lighted the start of the invasion once he found her.

Without warning, they did so, causing chaos with powerful monsters like "Antique Gear Chaos Giant" and sealing nearly all of the inhabitants of Heartland City into cards in the process. Yūto, Shun, Ruri and a few others were the only survivors of the attack including, although Ruri was captured not long afterwards.

In the aftermath, Barrett was sent to the ruined Heartland City on a mission with a few of his own comrades, but they were attacked by a "All-Purpose Landmine Glaymore" Trap Card. At some other point, a Synchro Dimension Duelist named Yūgo appeared in Heartland, looking for his friend who was kidnapped by the same person who captured Ruri, Yūri. However, he instead encountered Yūto and mistook him as the kidnapper while Yūto mistook Yūgo as one Academia Duelists. Their dragons fought each other until Yūto's allies appeared, at which point Yūgo retreated.

Seeking to avenge their comrades, Yūto and Shun traveled to the Standard Dimension and began attacking the members of Leo Duel School who used Fusion Summoning, sealing them into cards. Yūto attacked Shingo in defense for Yuzu Hīragi before learning that most students of LDS were oblivious to the situation, while Shun attacked LDS members indiscriminately, including Marco and Tio, sealing them into cards. Shun's attacks only stopped when he came face to face with Reiji Akaba, the person he had wanted to lure out the entire time, after a fight with Masumi, Hokuto Shijima, and Yaiba Tōdō, where the former was looking to avenge her teacher.

Shun was intent on defeating Reiji and holding him hostage so that Leo would release Ruri. However, Reiji told him that his plan was in vain as Reiji mentioned Leo would not be interested in rescuing Reiji, and instead proposed an alliance as they were fighting the same enemy, which Shun accepted.