While Ash and Leon battle the rampaging Dynamax Pokémon, Goh and Sonia seek answers about the legends of Galar and the Darkest Day. Then, Ash meets Chairman Rose, the president of Macro Cosmos. Rose supported Leon as a young Trainer, but when he makes a similar offer to Ash, our hero politely declines.
Meanwhile, Goh and Sonia share their findings with Sonia’s grandmother, Professor Magnolia. Professor Magnolia previously worked with Rose’s company to create the Dynamax Band, but she now fears that Rose is somehow involved with the rampaging Pokémon. When Goh and Sonia head out to do more research, they’re confronted by a mysterious man—what happens next?
Goh and Sonia reach the Turffield geoglyph, hoping to research its connection to the ancient hero legend and the current Dynamax outbreaks across the Galar region. Known as the Darkest Day, the Galar region was engulfed by a black vortex 3,000 years ago. A hero wielding the legendary sword and shield managed to quell the Dynamax Pokémon. Sonia speculates that the Darkest Day will reoccur, noting the similarly tough conditions they face today. Goh recalls his encounter with a Lugia, adding that a dark cloud appeared then as well. He theorizes that the dark vortex must mean the mysterious figure behind the Darkest Day is also a Legendary Pokémon, a connection Sonia hadn't considered before.
Following Giovanni’s orders, Team Rocket have infiltrated the underground Energy Plant as miners hoping to locate the evilest Pokémon. Oleana continues to inject more Galar Particles at the Energy Plant core, leading to more Dynamax events including a wild Coalossal. Chairman Rose is unfazed by the threats of Dynamax energy, declaring that soon Eternatus will be revived and save Galar's future. Ash and Leon soon arrive at the Energy Plant, the sight of a rampaging Gigantamax Coalossal. Using Gengar and Dragapult respectively, Ash and Leon manage to defeat Coalossal. The miners start throwing stones at the Coalossal, but Ash intervenes to protect the vulnerable Pokémon.
Meanwhile, Oleana's subordinate is shadowing Goh and Sonia's car. Sonia and Goh soon leave Turffield and head towards Wedgehurst, with Sonia learning that Goh was originally intending on meeting Professor Magnolia for advice on Dynamaxing. Goh is surprised to learn that Sonia is Professor Magnolia’s granddaughter. Sonia shows Goh several photos of the ancient tapestries located in the Hammerlocke Vault, believed to describe the origins of the Galar region. Sonia asks for Goh's insight, and Goh replies that the two depicted heroes might be the ones who fought against the Darkest Day. Sonia adds that the current retelling of the Hero legend may actually be wrong, and in fact two heroes may have worked together. Sonia declares that she will tell her grandmother right away, hoping that will be enough to become a Professor in her own right. She then backtracks, adding that Professor Magnolia is rather strict. Goh enquires into Sonia's motivations, leading Sonia to reveal that she and Leon were once friends. The pair left on a journey together, but they drifted after Leon's battling talents were spotted and he became a Champion. Sonia remarks that she could never defeat Leon in a battle, but decided to work with Pokémon in a different way.
Following the defeat of the Gigantamax Coalossal, Chairman Rose and Oleana introduce themselves to Ash. Leon reveals that Rose is the Chairman of Macro Cosmos, a company responsible for the supply of energy across Galar and the one who spotted his talents as a Trainer. Rose remarks that he has heard a lot about Ash from Leon, adding that he shows a lot of promise. Leon asks Rose if he knows anything about the Dynamax outbreaks, to which Rose denies having any knowledge. He suggests that the Dynamax outbreaks might just be a trial for a stronger future, though Leon insists that they need to stop things now to save the lives of people and Pokémon alike. The Chairman steers the conversation away from the crisis at hand, suggesting a commemorative dinner is in order. Ash’s grumbling stomach also agrees, while Leon suggests that it is a rather lucrative opportunity. Leon, meanwhile, is decides to investigate the Energy Plant for a connection to the Dynamax outbreaks. He believes Chairman Rose knows more than he was saying, recalling the suspicious comment made earlier.
Goh and Sonia arrive at Professor Magnolia's lab in Wedgehurst by evening. As they discuss their dreams, a Wishing Star crashes nearby. The rather stern Professor Magnolia appears, explaining that a Wishing Star appears to those with earnest dreams. She invites Goh inside, learning that he comes from the Cerise Laboratory and hoped to learn more about Dynamaxing. Magnolia reveals that Galar Particles are responsible from the Dynamax phenomenon, with links to Power Spots found right across the Wild Area that allow Pokémon to undergo Dynamax. She adds that Wishing Star a rich source of Galar Particles. Professor Magnolia reveals that she cooperated with Macro Cosmos and developed the Dynamax Bands as a way to control the Dynamax phenomenon. Sonia then enters the room, and present Goh with his very own Dynamax Band, fashioned using the crashed Wishing Star. Goh is thrilled with the gift. He then asks why can Pokémon only Dynamax in the Wild Area or in stadiums, to which Professor Magnolia clarifies that Power Spots are responsible for this. Professor Magnolia adds that she and Chairman Rose uncovered that Galar Particles can be used as an energy source, but stops short of elaborating any further. Sonia realizes her grandmother is hiding something, but Professor Magnolia denies it and changes the subject to Sonia's research task. Professor Magnolia takes a moment to review before commending her granddaughter's research, which sheds further light onto the Darkest Day and Galar Hero legends. Magnolia stops short of granting her granddaughter a pass, instead she wonders what happened to the sword and shield from the legend. While Sonia feels disheartened, Goh suggests this is an opportunity for them to uncover information about the sword and shield.
At Rose Tower, Ash and Pikachu are treated to a feast courtesy of Chairman Rose. Looking over the glistening Wyndon skyline, Rose remarks that is grateful for being lifted out of poverty and plans to preserve the very best that Galar has to offer. The comment catches Ash off-guard, but Rose quickly changes the subject again. He remarks that Ash certainly has promise as a Trainer and offers to use his resources to support Ash’s battling ambitions. Adding pressure, Oleana notes that Ash is lucky to receive such interest. Ash gives it some thought but ultimately declines, remarking that he wants to travel the world and forge his own path. Rose says nothing more, while Oleana is genuinely furious by Ash's disregard. Ash and Pikachu stay the night in the Rose Tower, placing a call through to Goh for an update. Goh reveals that he is at Professor Magnolia's lab, though he and Sonia plan on traveling to the Stow-on-Side ruins to discover more about the Darkest Day. Ash agrees to meet Goh there, ending the call.
The next day, as Sonia and Goh prepare to leave for the ruins, Professor Magnolia has a confession to make. She reveals that she broke off her partnership with Chairman Rose because she sensed his ill-intentions, adding that he will stop at nothing to achieve his goals. Professor Magnolia elaborates that she knows that Dynamax outbreaks have something to do with it, however she has no physical proof as of yet. She orders her granddaughter be quick in uncovering the truth, with Sonia and Goh both pledging to do their best. The conversation, meanwhile, is overhead by Oleana's subordinate who calls to inform Oleana of the new intel. Following orders, the subordinate trails Goh and Sonia undetected and directly to the mural at Stow-on-Side. He then makes his presence known, summoning his Gigantamax Garbodor to take care of Goh and Sonia. The presence of the Gigantamax Pokémon reveals the odd-looking mural to be a Power Spot and Sonia notices Galar Particles coming from the mural. To even the match-up, Goh Dynamaxes his Raboot, starting off with a direct Max Flare. Gigantamax Garbodor replies with G-Max Malodor, and the wake of stench knocks Raboot back, sending it crashing into the mural. As Raboot steps aside, Sonia quickly spots statues hidden behind, featuring two knights, as well as Zacian and Zamazenta.