Somewhere in Ultra Space, Necrozma emerges from a shattering mass of black crystals. It is attracted by the arrivals of Lunala and Nebby and flies towards them. Meanwhile, at Professor Kukui's house, Ash and his Pokémon wake up and notice Poipole looking around for something. At the same time, Ash finds Professor Kukui and Professor Burnet acting strangely exhausted and lethargic. Later, at the Pokémon School, Ash greets Sophocles, who is hungry after his mother overslept and didn't prepare breakfast. Then, the rest of the class arrives with similar stories of the adults being lazy and exhausted.
Just then, Kukui enters the classroom and lazily greets the class. He reveals that he was going to make the day's lesson about the Manalo Festival, but he doesn't feel like it and instead leaves the class to talk amongst themselves. He retires to the Principal's office, where Samson Oak is also tired and taking a nap, much to the concern of his Vulpix. Back in the classroom, Kiawe decides to take charge of the day's class. Kiawe explains that the Manalo Festival is in celebration of a solar eclipse that occurs every 21 years in Alola. Lillie asks about the Legendary Pokémon described in the myth and Kiawe replies that it is the "Blinding One". Ash and Poipole are surprised at the mention of the "Blinding One" and the former remembers Acerola's book, which Rotom brings up a picture of. Rotom adds that Poipole recently drew a picture of the "Blinding One". Lillie is instantly reminded of her mother's stories about the "Blinding One". At Mallow and Lana's insistence, Lillie tells the group about the legend. The "Blinding One" once appeared in the Pokémon world and filled it with overflowing light. The light, which held a mysterious power, led to the birth of the Alola region. However, the Blinding One ended up depleting its light, causing it to turn black and enter a long slumber. Then, the emissaries of the sun and the moon appeared and shared their light with the Blinding One, allowing it to awaken and shine once more, then it flew off to the ends of the sky.
The class figures the "emissaries of the sun and the moon" were Solgaleo and Lunala, and the "end of the sky" is the other side of an Ultra Wormhole. Kiawe wonders if the Blinding One is still on the other side of the Ultra Wormhole, and Lillie believes that it is. Poipole looks up at the sky to see dark clouds. Then, Komala rings the bell to announce lunchtime. After realizing his mother didn't make him lunch, Sophocles becomes depressed, but the class and their Pokémon share their food with Sophocles. Meanwhile, at Team Rocket's food truck, Meowth is excited about the eclipse, but Jessie and James aren't interested and feeling cold. Then, Meowth looks out to see people lazing around, including Nurse Joy and Officer Jenny. Mallow and Tsareena return home, but finds the place empty. Abe is revealed to have gone to Oranguru's place, along with several other tired adults. Meanwhile, at the beach, Ash and Kiawe try to practice their Z-Moves, but the moves fade away. Ash and Kiawe wonder what happened, and Rotom reveals that neither Pikachu nor Marowak were able to build up Z-Power. After Ash wonders if the clouds have anything to do with it, Poipole draws a symbol, the Prism Star, on the ground.
At Aether Paradise, Burnet is investigating the diminishing of Ultra Aura across Alola, and Faba wonders what's causing it. Wicke tells Faba not to speak before she does and Faba apologizes. Wicke apologizes for being so harsh and wonders if it's because she's in a downer mood. Then, Lusamine enters the room, with her hair all messed up, and wonders if the Ultra Aura diminishing is what's causing their lack of motivation. Burnet completes her analysis and brings up on a screen for everyone to see. The data shows a tiny Ultra Wormhole that is sucking up all the Ultra Aura. Wicke notes it is the opposite effect compared to when the Ultra Beasts appeared which caused the Ultra Aura levels to increase. As Lusamine proclaims that they'll need to investigate further, she and her staff collapse in exhaustion.
Meanwhile, a Team Rocket helicopter flies towards Alola. Inside, Matori informs Giovanni of the small Ultra Wormhole and that their target, the "Blinding One", might appear. Giovanni states that he expects great things from Matori and the transmission ends. At Gozu's command, the pilots activate the helicopter's optical camouflage to make it invisible as they approach Alola. Meanwhile, somewhere else, Gladion is trying to calm down his frightened Silvally. Gladion looks up at the sky and wonders if something is coming. Inside the Ultra Wormhole, Solgaleo and Lunala are rushing through as Necrozma follows after them. Solgaleo turns and attempts to confront Necrozma, but the latter fires Prismatic Laser, knocking Solgaleo out. Lunala sees this and continues to flee, with Necrozma in hot pursuit.
The next day, at the Pokémon School, the class notes how the dark clouds still haven't cleared, when Komala rings the Ultra Guardians bell. Seeing as Kukui is not there, Ash decides to press the button himself. At the base, the Ultra Guardians are greeted by a tired Lusamine. Lillie gets embarrassed by her mother's untidy appearance and says that she should properly groom herself before appearing in front of people. Lusamine lazily instructs the Ultra Guardians to head for the Altar of the Sunne. Mallow asks if another Ultra Beast appeared, but Lusamine replies that she'll tell them when they have arrived. To the Ultra Guardians’ surprise, Lusamine adds that she'll meet them there. With Lusamine forgetting to send the group off with a finishing line, Ash takes charge and the group sign off with an "Ult-Roger!".
At the Altar of the Sunne, the Ultra Guardians arrive and meet up with Lusamine, Wicke, Faba, and Burnet. Lusamine tells the Ultra Guardians that their seventh member should appear soon. As Ash asks, they group feel a gust of wind as a Ride Noivern descends with Gladion, in a slightly different Ultra Guardians uniform, arrives on the scene. Ash and Lillie are happy to see Gladion, who explains that Silvally was frightened and that if there's an Ultra Beast, then it might be the most dangerous one yet. Gladion then notices Poipole, which Ash confirms is an Ultra Beast. Kiawe asks about their mission, and Lusamine calls for Burnet to explain. Burnet states that the Ultra Aura in Alola has been decreasing, and Wicke believes that's why the adults' motivations are dropping as well. Lusamine states that children and Pokémon aren't affected for some reason. Burnet and Wicke detail that the Ultra Aura decrease is being caused by a small Ultra Wormhole that opened close by. Gladion asks about the chance of an Ultra Beast appearing and his mother replies it's possible if the Ultra Wormhole grew bigger. Burnet replies they are trying to find the Ultra Wormhole. Wicke calls for Faba, but he is more focused on his game console, forcing Wicke to shout to get his attention.
Faba says the clouds are in the way of finding the Ultra Wormhole and reveals a machine that can disperse the clouds. He states that the Ultra Guardians can use their Z-Moves to power the machine in order to clear the clouds. Ash and Kiawe state that they weren't able to perform Z-Moves the day before which Burnet explains is because Z-Power is linked to Ultra Aura. Faba states that even with less Z-Power, four Z-Moves might provide enough power for the machine, so Ash, Kiawe, Lana, and Gladion have their Pokémon use their respective Z-Moves to build up Z-Power and fire it at the machine. The machine powers up and successfully blows the clouds away. As Burnet gets to work, Lusamine escorts the Ultra Guardians to a recently discovered ruin. Inside the Altar of the Sunne, a mural depicting the Blinding One, Lunala, Solgaleo, several Trainers and their Pokémon using Z-Moves, and the Prism Star symbol that Poipole drew. Lusamine focuses on the mural's ancient text, she believes that it holds more information about the legend. The Ultra Guardians' bracelets call for them to return.
Back outside, Burnet reveals that they found the Ultra Wormhole, but it's getting bigger. In front of the moon, the Ultra Wormhole fully opens as Gladion sends out Silvally. Then, Lunala appears, much to everyone's surprise and amazement. But then, Silvally gets frightened again as Lillie wonders if Lunala is the cause of the Ultra Aura drain, but Gladion states it's not Lunala and that something else is coming. To everyone's surprise, dark energy crackles as Necrozma also emerges from the Ultra Wormhole.