A young thirteen-year-old Reiji stumbles through an inter-dimensional portal to find out why his father keeps disappearing for long periods of time. Reiji encounters Serena being chased by four men and helps her out, only for the both of them to be cornered later. Through listening to Serena arguing with Leo Akaba, Reiji learns that his father is waging war on other dimensions, before being sent home.
In the present, Reiji offers Serena a place fighting against Leo Akaba at his side, but she turns him down, explaining that she wants to prove her strength to the Professor so hell stop holding her off the battlefield. Reiji lets her go, denying any knowledge of Kurosaki and warning her that hell interfere if she makes herself a nuisance.
The next day, everyone shows up to the next round of the tournament - except Kurosaki - and are shocked to learn its a city-wide duel with Action and Pendulum cards scattered throughout the city. Everyone has twenty-four hours to find two Pendulum cards and win two more Pendulum cards from another duelist. Meanwhile, Reiji and Himika talk about how the entire thing is a front to prevent an attack from Fusion. Instead of letting people know that they might soon be facing an inter-dimensional army and causing city-wide panic, theyre keeping people safely indoors with the city-wide duels and letting them think that any disruptions are just part of the tournament. Meanwhile, the eight best students from the Youth class are being dispatched through the city to fight off any actual invaders.
Back in the Fusion Dimension, Leo Akaba summons Sora. Hes sending Sora back to Standard to capture Serena. Joining Sora will be a group known as the Obelisk Force.
This episode provides examples of:
- Befriending the Enemy: Reiji tries this with Serena.
- Blatant Lies: I have no idea if there are any Xyz remnants in this dimension.
- Curb-Stomp Battle: Kurosaki's duel with the Knight of Duels student is described as "one-sided", unsurprisngly.
- Hidden in Plain Sight: How does Reiji plan to hide the army using Duel Monsters to invade? By having Action Duels go on all throughout the city!
- Skewed Priorities: Yoko is apparently unsure whether to cheer for her own son or Michio, the chef she fangirls over.
- Too Clever by Half: Yuu seems to consider Kurosaki this, after the latter says the Top 8 Youth students aren't going to last long against the invasion.
- "Well Done, Son!" Guy: A non-parental example, as despite being kept locked up, it seems all Serena wants is to prove her strength to the Professor.
- Whole Plot Reference: Downplayed. As with the previous Yugioh show, the tournament contains a section very similar to the Battle City format, this time including cards that need to be gathered. However, it's implied that this wouldn't have been the case if not for an impending invasion, and unlike Battle City and the WDC where the Battle Royale was at the beginning to quickly pick off a lot of contestants, this is for the Top 16.