During a confrontation at the Stow-on-Side mural, Sonia quickly spots statues hidden behind, featuring two knights, as well as a pair of mysterious Pokémon - Zacian and Zamazenta. Oleana's subordinate, however, orders his Gigantamax Garbodor to attack with Max Steelspike. Goh's Raboot takes the hit before retaliating with Max Knuckle, sending Garbodor crashing down. The Macro Cosmos agent orders his Garbodor to get up immediately and attack with G-Max Malodor. However Raboot’s Max Flare lands first, knocking Garbodor out. The agent immediately recalls his Pokémon and flees the area. Raboot returns to its usual form, with its performance in battle earning Goh and Sonia's praises.
After staying the night at Rose Tower, Ash leaves aboard his Dragonite to meet Goh at Stow-on-Side. Meanwhile at the mural site, Goh examines the uncovered statues and reveals that he recognizes one of the mysterious Pokémon, Zamazenta who he encountered in the Slumbering Weald. He adds that his Poké Ball simply went through it and he later woke up alone amongst the thick fog. Sonia and Goh soon notice a plaque, revealing the names of the mysterious Pokémon to be Zacian, the one holding the sword, while Zamazenta is holding the shield. Sonia concludes that the ancient legend that surrounds the Darkest Day is wrong, and that two heroes alongside two Pokémon overcame the crisis 3,000 years ago. Recalling the Turffield geoglyph, Goh deduces that the "Darkest Day" was in fact a Pokémon, to which Sonia agrees. A group of Macro Cosmos agents arrive on the scene, though Goh and Sonia charge towards them to escape another confrontation. The pair rush to Sonia's car, buckling up and driving to the Slumbering Weald to ask for Zacian and Zamazenta's help in solving the Dynamax outbreaks across Galar. On the way over, Goh phones Ash to change their meet up arrangements to the Slumbering Weald and updates him on all his latest discoveries about the ancient Galar legend surrounding the Darkest Day.
Leon, meanwhile, continues to investigate the Energy Plant for clues about the current Dynamax outbreaks and Chairman Rose's suspected involvement. He soon reaches the tower summit, just in time to see the energy core become overloaded from an injection of Galar particles. Several beams of red light shoot across the sky, capturing Ash's attention. The Rotom Phone reveals that the source of the red light is somewhere in Hammerlocke. Fearing more Dynamax outbreaks will occur, Ash decides he will investigate the red lights further. Goh agrees to the change of plans, adding that he and Sonia will continue onto the Slumbering Weald to recruit Zacian and Zamazenta.
A Pokémon finally bursts from the Energy Plant reactor core, revealing it to be Eternatus. As one of the Macro Cosmo employees makes a call direct to Chairman Rose, Leon realizes that the Chairman is behind all of the Dynamax outbreaks. Frustrated, Leon calls out his Charizard to battle Eternatus and stop it from escaping. However, Eternatus flies upwards and emerges inside the Hammerlocke Stadium above. Team Rocket, on a mission to capture Eternatus for Giovanni, remove their mine worker disguises before Meowth launches a rocket-propelled net at it. Eternatus replies with a beam of Dynamax energy, striking Meowth and causing him to Gigantamax. Jessie and James are thrilled with Meowth’s powerful new form and order him to attack. Meowth, however, attacks his teammates in a Gigantamax-induced rage. Ash and Dragonite reach Hammerlocke Stadium to see Team Rocket fleeing from Gigantamax Meowth. Jessie and James order Ash to do something about it.
The confrontation at Hammerlocke Stadium is filmed by a passing news crew, with the footage streamed directly to Sonia's Rotom Phone just as she and Goh have reached the Slumbering Weald. Transmission suddenly cuts out as Eternatus fires off another attack. Realizing the Darkest Day has actually been revived, Goh and Sonia push ahead to locate Zacian and Zamazenta. Goh and Sonia call out into the fog, and before long, Zacian and Zamazenta arrive on the scene. The two legendaries then turn away and appear to vanish into the thick mist. Goh is initially disappointed, but Raboot senses something up ahead. The trio soon arrive at an altar, and locate the Rusted Shield and Rusted Sword lying there from the ancient legend. Goh packs the ancient artefacts in his bag, as he and Sonia set their sights on reaching Hammerlocke.
Inside Hammerlocke Stadium, Eternatus attacks Ash's Dragonite, leading Ash to recall it for a rest. Leon and Charizard then arrive on the scene, before Chairman Rose makes an appearance. Rose proudly announces that Eternatus, whom he named for its "infinite" energy, is in fact the fearsome Darkest Day from the legend. Eternatus tries to escape, however the stadium’s audience safety barrier is helping to keep it contained. Rose reveals that Galar was due to exhaust all of its energy sources. However, Eternatus offers incredible energy and will be key to securing Galar's future. He explains that Eternatus actually creates Galar particles. Leon urges Rose to consider the threat Eternatus and its energy poses. Rose, however, announces that helping recruit strong Trainers like Leon has been part of his plan, clarifying that he wants Leon to catch and control Eternatus. Rose explains that his father once worked in the mines to extract energy, though he eventually passed away following an accident on the job. The loss of his father motivated him to find a more viable energy source like Eternatus, where no one will need to suffer like he did. Leon seemingly complies, agreeing to catch Eternatus as requested. Rose is grateful for Leon’s loyalty. However, Leon clarifies that he will catch Eternatus to calm it down. Just then, Eternatus uses Dynamax Cannon, blasting through the safety barrier and flying to the top of the stadium, where it begins to charge itself up with Galar particles. Leon insists that Eternatus is far too dangerous, so he’ll have to catch and seal it away.
Rose is disappointed by his star prodigy's sentiments and calls out Copperajah to attack. Ash makes the first move, having Pikachu strike with Iron Tail. He urges Leon to focus on catching Eternatus, and the Galar Champion complies, leaving Ash to face-off against Rose. The Chairman calls out his Ferrothorn, so Ash summons his Riolu to even things up and make it a Double Battle. While Team Rocket are still being chased by their Gigantamax Meowth, Sonia crashes through the stadium safety barricade and urges Goh to rush ahead to help Ash out. Sonia is confident she can take on the Macro Cosmos agents by herself, but is quickly feeling intimidated by the quartet of Steel Pokémon she has to battle. Luckily, Raihan arrives on the scene and calls out his Duraludon to assist. Goh, meanwhile, is stopped by Oleana. Her initial smug demeanor turns to anguish when Goh insists he must stop Chairman Rose, and Oleana summons her Milotic. Oleana adds that as secretary she must defend Rose's dream, adding that Rose has spent too much time and effort to see it fail. Goh is unfazed by Oleana's intimidation tactics and selects Raboot to battle.