Following their adventure in the Galar Mine, Liko, Roy, and Friede have returned to the Brave Olivine with the mysterious Pokémon that emerged from Liko's pendant. With none of the Rising Volt Tacklers or even the Pokédex recognizing it, Liko, Roy, and Friede head out to ask more from Liko's grandmother. Friede also asks Captain Pikachu to watch over the airship while they're gone. Meanwhile, Amethio has contacted Hamber to reveal that he's been operating on his own. He also reveals footage of the mysterious Pokémon that emerged from the pendant they've been trying to obtain. Hamber is surprised to see this and accepts Amethio's request to resume pursuing their target, which Amethio reveals yo be currently headed for Hammerlocke. Amethio ends the call, and Hamber starts contacting other Exolorers admins. Spinel and Agate too busy to answer, but Onyx and Sango accept the call to head to the Galar region with him. The two start to argue, but Hamber's Dusknoir scares them back in line as they head out.
Liko, Roy, and Friede arrive in the Wild Area, but before they can decide which of the area's numerous castles to investigate, Liko's grandmother's Squawkabilly approaches them, repeating the words "Liko" and "old castle", prompting the trio to follow it. Squawkabilly eventually leads them to what looks like a wall of stone, until a Stonjourner moves aside to reveal a secret passage for them. They go inside and Stonjourner moves back to cover the entrance again, leaving Zirc and Onia confused about where their targets disappeared to when they arrive in the area moments later. While Amethio arrives to help them in their search, Liko tells Roy and Friede more about her grandmother. She has never seen her more than during brief visits, which she doesn't necessarily even count as proper meetings, the last of which happened a year earlier when Liko was accepted into the Indigo Academy and her grandmother visited her to give her her pendant as a good-luck charm.
Eventually, the Rising Volt Tacklers trio arrives at the old castle they were searching for. Liko calls out to her grandmother, and is right away greeted by her grandmother's Arcanine and then her grandmother, Diana, herself. Roy and Friede introduce themselves to Diana, while Liko introduces her to her partner Pokémon, Sprigatito. Diana shows them around the castle, which serves as one of her hideouts and as a spot where wild Pokémon can come and go as they please. Sitting down to talk, Diana reveals that she too had been targeted by the people after her pendant and thanks Liko for keeping it safe. Liko and Friede struggle to explain the situation, but before they can properly do so, the truth reveals itself when the mysterious climbs out of Liko's bag and moves towards a surprised Diana. Liko explains that her pendant transformed into this Pokémon, which Diana identifies as Terapagos. While she knows the Pokémon's name, she hadn't expected the pendant to be a hibernating Terapagos, even if its form differs from the recorded form with a big shell. She also suspects that Terapagos used to be one of Lucius's partners, much to Liko and Friede's surprise.
Back at the stone wall, Amethio notices one spot looking off and has Ceruledge use Psycho Cut on it, sending the Stonjourner running off and exposing the secret passage. At the castle, the group eats a meal of canned food and follows it with cups of tea. Liko asks Diana to tell her how she became an adventurer, which she's happy to tell now that Liko has taken her own first step into the world. When she was even younger than Liko is now, she had discovered an old briefcase in her attic. Inside it, she had discovered the pendant and a book written by Lucius about his adventures. This inspired her to start her own journey to learn more about Lucius, but no matter how hard she searched, she never found a single sign of him. 30 years ago, she finally gave up on her search, but still keeps on adventuring, all thanks to the inspiration provided by Lucius. Several months ago, an old friend of hers offered to support her on her adventures, but when it turned out that said friend was associated with a shady organization that was after her pendant, she chose to hire the Rising Volt Tacklers to protect both Liko and the pendant. She thanks Friede for protecting her granddaughter. Roy shows Diana the Ancient Poké Ball which the Black Rayquaza had emerged from. Liko also recounts how some mysterious visions had appeared during their encounters with Arboliva and Galarian Moltres, which she now suspects were actually Terapagos's memories. When she asks her grandmother if she knows what "Rakua" is, Terapagos suddenly lets out an excited cry and moves towards a nearby door. Diana answers that Rakua is the name of the paradise that Lucius sought and leaves to fetch something she wants to show them: Lucius's memoirs.
However, whilst Diana is on her way to retrieve the memoirs, her Arcanine and a Blipbug appear behind a window to warn her that intruders are approaching. Moments later, Amethio, Zirc, and Onia enter the building. Friede sends out his Charizard, while Amethio calls out Ceruledge, and Zirc and Onia cover Liko and Roy's escape routes. Terapagos notices Amethio and pulls itself free from Liko's grasp, locking eyes with him and letting out a sharp cry.