Ash and his classmates continue to prepare their individual projects on Poni Island. Kiawe has his Marowak and Turtonator practice some battle techniques. Sophocles is in the middle of strengthening Charjabug before he evolves it, while Mallow scours the Seafolk Village markets for new ingredients and Lana does some fishing while she waits for Ida to arrive. Meanwhile, Lillie and Snowy are busy documenting the Pokémon that live on Poni Island.
Meanwhile, Ash decides to challenge Hapu, but he finds her home empty. Ash then sees Nurse Joy and asks if she knows where Hapu is. Nurse Joy replies that she might be at the Ruins of Hope. At the ancient ruins, Hapu is praying at the altar, hoping to hear her grandfather's voice for guidance. Hapu declares that she wants to be the Poni Island kahuna and does not understand why Tapu Fini has not ordained her into the role yet. Her pleas, however, remain unanswered. Meanwhile, Lillie spots a wild Trumbeak and takes a photograph of it, followed by a Gumshoos, Pinsir, and a sleeping Granbull. Snowy runs off after sensing something, and leads Lillie to her older brother Gladion, who is training with his Pokémon.
Meanwhile, Hapu returns to her Mudsdale's side disappointed to have not received any answer as the tide rises and covers over the entrance to the Ruins of Hope. As Hapu and Mudsdale head back home, Mudsdale steps on something and suffers sharp pain in its hoof. Ash makes his way through the Poni Breaker Coast's rugged terrain and soon sees Hapu clinging onto her bucking Musdale's tail as it cries in pain. Hapu is unable to explain Mudsdale's berserk behaviour, but Ash spots something in one of Mudsdale's front hooves. He orders Pikachu to use Iron Tail and it dislodges a Corsola horn fragment from Mudsdale's hoof. Mudsdale is instantly relieved of its pain, and while Hapu is grateful for Ash's assistance, she expresses her disappointment for not noticing the problem. Hapu then asks Ash how she can repay him. Ash instantly points to her Z-Ring, but Hapu pulls her wrist away and exclaims that she received it from her grandfather. Ash says that he doesn't want the ring but a battle.
Overlooking Seafolk Village, Lillie and Gladion talk among themselves. Gladion explains that he is hoping to challenge Tapu Fini in a grand trial. Lillie immediately chuckles to herself and adds that Ash has the exact same idea. Gladion smirks, then he admits that he also wanted to visit Tapu Fini because it can supposedly allow a person to see a deceased loved one. He clarifies that he wishes to meet their father. Lillie is shocked by the confession, then the wind suddenly picks up and blows her hat away. Gladion looks down as Lillie stares at him for a silent moment, then Umbreon returns Lillie's hat to her. Lillie recalls that their father passed away in an accident while researching Ultra Wormholes. Gladion admits that he doesn't remember the details because he was quite young, and only recalls his father patting him on his head. Lillie confesses that she only knows their father's face from photographs, and never asked Lusamine about him. Gladion remains hopeful that Tapu Fini will recognize his strength as a Trainer and grant him his prayers. Lillie perks up and offers to battle Gladion to help summon Tapu Fini, and Gladion agrees to the idea.
Ash follows Hapu and her Mudsdale on foot, and again asks her for a match. Hapu knocks back his offer and states that she doesn't battle for fun. Ash asks why she battled him the previous day, and Hapu explains that she thought Ash was a radish thief. Hapu tells Ash that he could just battle his classmates. Ash explains that he wishes to go up against many different Trainers to help him prepare for his grand trial against Tapu Fini. Hapu is immediately infuriated and scolds Ash for not knowing what a grand trial actually is. She tells him to cleanse himself before having Mudsdale kick Ash, Pikachu and Rotom away. Ash lands in the middle of Gladion and Lillie, who are about to start their battle. Gladion and Ash are shocked to see each other, and Ash goes on to explain that Hapu's Mudsdale kicked him after he asked for a battle against her. He goes on to call Hapu "stubborn", but she overhears the snide remark and chases him around on her Mudsdale. Lillie calls for the pursuit to end, allowing Ash to catch his breath. Lillie then formally introduces herself and Gladion to Hapu, who is immediately impressed by Lillie's good manners. Hapu spots some holes in Gladion's clothing and asks if she can mend it for him, though he dismisses her request and goes on to ask Ash for a battle. Lillie is fine with the idea and thinks that the heated match will help summon Tapu Fini. Ash pleads with Hapu to stay and watch the battle, though she is none too pleased. Gladion then asks Ash if they can have a battle between their Lycanroc, and Ash is immediately excited by the prospect.
Hapu declares herself the battle judge. She then sees Ash's Lycanroc's unusual orange coat, and Rotom explains that it is a Dusk Form Lycanroc. Hapu frowns and wonders who Ash is, she then calls for the one-on-one battle to begin. Ash has his Lycanroc make the first move, an Accelerock. Gladion orders his Lycanroc to Counter the attack. The two Lycanroc engage in a tense confrontation before being sent backwards, with Ash's Lycanroc flying into a nearby cliff. Gladion is surprised that Ash's Lycanroc withstood the damage and immediately recognizes its unusual strength, Ash has his Lycanroc charge forward with another Accelerock. It leaps onto the rock cliffs to launch its attacks, but Gladion's Lycanroc evades several times. Ash then calls for a Bite attack, but Gladion's Lycanroc jumps up and forces its opponent to the ground. Gladion is glad to see that Lycanroc has improved since last time they battled and Ash admits that Tapu Bulu helped Lycanroc to overcome its fear of dirt. Hapu is immediately taken aback by the confession and remains determined to learn who Ash really is. She turns to Lillie and declares that the ongoing battle is far different from anything she has ever witnessed. Lillie states that she has learned a lot from Ash, and informs Hapu that the role of an island kahuna helps to bring out a Trainer and their Pokémon's strength.
The battle continues, and Ash's Lycanroc lands a successful Stone Edge on its opponent. Gladion has his Lycanroc power up with Swords Dance and strike back with Outrage. Ash calls for another Accelerock, and it clashes several times with Lycanroc's Outrage attack. The two trade blows before Ash has his Lycanroc attempt a Bite attack to stop Gladion’s Lycanroc from moving. Lycanroc pre-empts the strategy and swats Ash's Lycanroc away. While Ash's Pokémon looks battered, Gladion's Lycanroc is afflicted with confusion because of its exhaustive Outrage attacks. Ash used the delay to perform Lycanroc's exclusive Z-Move, Splintered Stormshards. The powerful move lands on Gladion's Lycanroc, but when the dust clears Lycanroc remains standing. Rotom goes on to explain that the Z-Move also helped Gladion's Lycanroc to snap out of its confusion. Gladion then reveals his new Dragonium Z and has Lycanroc perform Devastating Drake. The winged dragon of energy strikes Ash's Lycanroc, taking it out of the fight, and Gladion is officially declared the winner of the match.
Ash rushes over to his Lycanroc, and is relieved to see that it's well considering its defeat. Gladion and his Lycanroc fist-bump each other. Ash then declares that he will catch up to Gladion and win next time, and Gladion smiles in response. Hapu continues to consider the intense battle she had just witnessed. Suddenly, everyone hears a cry overhead and it turns out to be Tapu Fini. The island deity flies over the group, almost foreshadowing a brighter future for them all.