Ash and his Pokémon do some push-ups on their boat while they wait to arrive on Ula'ula Island. Rotom soon alerts Ash that their destination is up ahead. In a flashback, Ash recalls that Professor Kukui revealed to his students that he dreamed of opening the Alola Pokémon League and required their assistance to make it a reality. Both Ash and Kiawe had gotten fired up by the news and decided to take part in the League.
On the island, Jessie and Mimikyu admire their new Z-Ring, much to the disappointment of Meowth and James, who are eager to use it with Mareanie. Jessie's posing is interrupted by Mimikyu, who spots Ash and his Pokémon as they arrive on Ula'ula Island. Team Rocket realizes that Ash has traveled alone, and with their new Z-Crystals, they may very well defeat him in battle. Meanwhile, Bewear remains unaware that Team Rocket is away and has left their button-eyed robots back at the hideout.
Nanu walks sluggishly past the Po Town Police Office, yawns, and plans on taking a nap. He is soon confronted by Officer Jenny and Oricorio, who have come to check on him. Nanu denies that he was planning on taking a nap and turns back to the police station. Jenny salutes him as he returns to his hungry and meowing Alolan Meowth. He quickly feeds them, but his relaxation is again interrupted by a phone call from Giovanni. Giovanni admits that he was surprised to learn that Nanu became a police officer and an Island Kahuna, before asking him about the "Blinding One". He ignores Giovanni's query and hangs up after hearing someone calling for him from outside.
Nanu steps out of his office to see Ash smothered by his Alolan Meowth. Poipole shoots out some red sludge, though the Alolan Meowth respond by scratching it, which then turns into a full-blown melee. The find soon ends with Rotom scolding Poipole for sparking the fight, and Nanu comes to Ash's assistance, criticizing his conduct. Ash stands up immediately and greets Nanu, hoping that he is the Island Kahuna. Nanu attempts to lie to Ash, stating that the person Ash is looking for is one of his coworkers who is busy on patrol. Ash formally introduces himself, while Nanu admires his rare Poipole and Lycanroc. Poipole squirts some red sludge onto Nanu, though Ash has Poipole apologize for its actions. Nanu invites Ash into the police station so he could clean himself up. Upon seeing his Alolan Meowth hungry again, Nanu asks if Ash could feed and play with them while he waits for the Island Kahuna to arrive. Ash agrees, while Nanu leaves for someplace. While Ash is bitten and scratched, Rotom and his Pokémon, except for Torracat, enjoy the playtime and are left exhausted.
Acerola and her Mimikyu, Mimikins, enter the police station, looking for Nanu, though she instead finds Ash and his Pokémon. Ash explains that he was waiting for another officer to arrive, but Acerola laughs and reveals that her uncle Nanu is the only stationed officer. Rotom is sent into a spin after he tries to take pictures of Mimikins, but all of the photographs come out with an odd haze. Acerola reveals that Mimikins is an actual ghost, much to Ash and Rotom's surprise. Acerola escorts Ash to her workplace, the Malie City Library.
Poipole is enthralled by its book-filled surroundings, though it soon stops flying around to focus on a page that depicts Ultra Necrozma, with Lunala and Solgaleo standing on either side of it. Acerola explains the legend of the "Blinding One", a Pokémon said to shine brighter than anything else in the world. She details that when Alola had just formed, it was entirely dark, but the arrival of three Legendary Pokémon showered the area in light. As a result, the people of Alola were immensely grateful for the "Blinding One's" efforts and have continued to pass on the story throughout the generations. Acerola states that Nanu believes that the "Blinding One" may be an Ultra Beast. Team Rocket happens to overhear the conversation from outside and looks forward to revealing the new information to the Boss.
Sometime later, Ash is busy feeding Rowlet as his other Pokémon play with Mimikins, while Acerola is working at a kitchen bench. Ash tries to catch up with Nanu, but Acerola assures him that Nanu won't be there. She then reveals that she has taken his favorite play-toy, a kendama, as a hostage. Right on cue, Nanu walks through Acerola's door in search of the kendama, though he is initially startled to see Ash. Irritated that his cover was blown, Nanu ignores Ash's challenge. However, with Acerola's glare, Nanu concedes and decides to test Ash's skill in a pre-trial.
Acerola officiates the match, acting as a referee. Ash asks Nanu to give him a good fight, but he sighs and sends out his Krookodile, who immediately uses its Ability Intimidate on Ash's Lycanroc. Ash starts off the battle, having Lycanroc use Tackle, which Krookodile knocks back with its head. Krookodile continues to intimidate Lycanroc, who bares its teeth, which Nanu is glad to see. Lycanroc follows up with a Rock Throw, but Krookodile swats the attack away with its tail. Pikachu uses Iron Tail to stop the debris hitting Acerola. Lycanroc's Bite fails and Krookodile responds with a Sand Tomb, which traps its foe in shifting sands.
Krookodile lands several Mud-Slap attacks on Lycanroc, though its predicament only angers Lycanroc, whose eyes begin to glow red. Ash is immediately concerned by the change and remembers his battle against Gladion. Lycanroc suddenly leaps into the air and crunches down on Krookodile's arm. While Krookodile shakes it off, Lycanroc again bites down on its foe, but receives a hit to the face. Lycanroc continues to disobey Ash, while Nanu has Krookodile continue to face the enraged onslaught. Nanu finally responds, having Krookodile use Counter followed by Crunch, doing serious damage to Lycanroc. Acerola calls the match off as Ash makes his way to his injured Pokémon. Nanu tells Ash to return to Melemele Island, but Ash disagrees and vows to remain on Ula'ula Island to train for a rematch. Nanu shrugs and sighs as he walks off.
Meanwhile, Team Rocket reports their latest findings on the "Blinding One", though Matori informs them that the information was already known to Giovanni. Matori's dismissal and quick ending of the call sends Jessie into a tirade. James pitches in that they need to catch Pikachu, setting the trio's sights once again on their long-term target.
At Acerola's house, Ash notices Lycanroc is upset while the other Pokémon eat their food. Sitting beside it, Ash admits that he shares Lycanroc's sentiments, and affirms that there was nothing he or Lycanroc could do. He then asks Acerola for an ideal training location on Ula'ula Island. She responds that Tapu Bulu could help them train, and Rotom points out they met it once before. Ash is immediately excited by this, and offers Lycanroc a mountain of food in preparation for its intense training. In agreement, Lycanroc takes a large mouthful of food from Ash's hand.
Back at his office, Nanu plays with his kendama, which hypnotizes his Meowth, who watch on and trace his movements with their heads in amazement. Nanu stops fidgeting and grins as the sight of his entertained Pokémon.