In Faba's Revenge!, it was lured out of Ash's bag by Faba, who convinced it to teleport him back to Aether Foundation's sealed lab. After arriving, Faba captured it in a device designed to keep it from teleporting. Faba intended to use Nebby's power to open an Ultra Wormhole, but he was stopped by Ash's Pikachu and Gladion's Umbreon. However, after being released, Nebby evolved into Cosmoem, and the residual energy from the evolution caused a Wormhole to appear anyway.
Nebby traveling through an Ultra Wormhole
Nebby was brought to the Altar of the Sunne by Ash in Family Determination!. In the next episode, Ash gave Nebby to the Tapu, asking for their help. After being blessed by Tapu Lele and Tapu Fini, the four deities sung at the Altar, opening the mechanism within and causing Nebby to evolve into Solgaleo, much to the surprise of everyone present. After greeting the others warmly, Solgaleo accepted Ash, Lillie, and Gladion's plea to help Lusamine, giving Ash a Solganium Z. After having his Z-Ring upgraded to a Z-Power Ring by the Tapu, Ash and the others climbed on Solgaleo's back, and using the power of the Z-MoveSearing Sunraze Smash, created an Ultra Wormhole to travel to the place Lusamine awaited them.
After arriving in the Ultra Deep Sea in Rescuing the Unwilling!, Solgaleo and Ash cornered Lusamine during the following episode. As a result, Lusamine flooded their island with a poisonous liquid. Due to Solgaleo's Steel-type giving it immunity to poison, it protected Ash from the liquid, and then carried him across it, dodging Lusamine's attacks along the way. After that, it went back with Ash's Lycanroc to help the others fight off Lusamine's Pokémon, who continued to heal themselves due to the Nihilego's energy. Everyone later succeeded after Lusamine was freed from Nihilego's control by Ash. Solgaleo then carried the group, now joined by the revived Lusamine, back to the Altar of the Sunne. After the conclusion of the episode, it parted from the group.
In Full Moon and Many Arms!, Solgaleo arrived in Alola, where it met up with Ash again and fought Dawn Wings Necrozma in an effort to free Lunala from its control. With its Sunsteel Strike, Solgaleo managed to knock Necrozma off of Lunala, causing it to break apart and fall into the sea. Shortly after, the elite Team Rocket unit, the Matori Matrix, attacked Solgaleo and Lunala by trapping them in an electrified net. After being freed by Ash's Pikachu and Gladion's Silvally, Solgaleo retaliated by attacking the unit's aircraft, forcing them to retreat. Immediately after, Necrozma emerged from the sea and possessed Solgaleo, causing it become Dusk Mane Necrozma. Ash tried to free Solgaleo, but was unable to stop Necrozma, and it fled into an Ultra Wormhole.
In The Prism Between Light and Darkness!, Solgaleo remained fused with Necrozma. The Ultra Guardians, with Lunala's help, pursued Necrozma to Ash's Poipole's home world, and learned that Necrozma was preying on the two Legendary Pokémon in order to absorb their light and restore itself to its Ultra form. After being asked by Nagandel to save Necrozma, Ash, Kiawe, Lana, and Gladion attempted to use their Z-Moves to supply Necrozma with Ultra Aura and separate it from Solgaleo. However, they were only successful in making it more powerful. Communication between the Guardians and their home base was soon reestablished. After Lusamine, Wicke, and Professor Burnet shared what they knew, they arranged for the people and Pokémon attending the Manalo Festival to follow the lead of the guardian deities and share a portion of their Ultra Aura with Necrozma. Combined with the Ultra Aura of the Ultra Guardians and their Pokémon, Necrozma received enough light to separate from Solgaleo. Solgaleo then joined forces with Ash, Gladion, and Lunala, giving Necrozma one last boost of power with the combined Ultra Aura of their signatureZ-Moves, Searing Sunraze Smash and Menacing Moonraze Maelstrom. Through these efforts, Necrozma's strength was finally restored. After Ash and Pikachu bade farewell to Poipole, Solgaleo and Lunala led the Ultra Guardians back to Alola.
In the original Japanese version of the anime, Nebby's official nickname is simply ほしぐもHoshigumo, as opposed to Hoshigumo-chan. The -chanhonorific is still used occasionally, with "Little Nebby" being used instead of Hoshigumo-chan in the English dub. In Now You See Them, Now You Don't!, Team Rocket caught sight of the unidentified Pokémon while Ash was buying donuts from their food truck. James surmised that the unknown Pokémon was the pre-evolved form of Koffing, and named it Protokoffing (Japanse プチドガースPuchidogars). This led to confusion when the trio saw Cosmoem in Revealing the Stuff of Legend!, causing James to assume that there was an intermediary phase it evolves into in Alola, which he dubbed Nanokoffing (Japanese カタドガースKatadogas), but this was ultimately debunked when they witnessed "Nanokoffing" evolve into the Legendary Solgaleo. After its final evolution, Ash and his classmates typically refer to it by its proper name, Solgaleo.
As a Cosmog, Nebby shared many traits with human babies. It slept and cried a lot, but was easy to amuse and was naturally curious. Its cries were quite powerful, and they caused nearby people and Pokémon to cover their ears. In A Masked Warning!, its cries were so powerful, it sent Pikachu flying back into a tree. Nebby was a very fussy eater and appears to have a preference for star candy (Japanese コンペイトkonpeitō). It was also ticklish and enjoys playing hide-and-seek, as shown respectively in A Dream Encounter! and Night of a Thousand Poses!.
In Now You See Them, Now You Don't!, it was shown that Nebby tends to teleport people to places they are thinking or talking about. Rotom surmises this is because it knew little about the world around it, so it had to depend on telepathy and other people to develop its abilities. By the end of the episode, it had become attached enough to Ash, to the point where it would willingly teleport to him on its own whenever they are separated.
After evolving into Cosmoem, Nebby hardly spoke, moved, or emoted, reflective of its coccoon-like state. However, after evolving into Solgaleo, it appeared to have grown into a more mature version of itself physically and mentally, letting Lillie hug it, happily accepting the Star candy from Ash, and licking him affectionately. As a Solgaleo, it can create Ultra Wormholes at will with the help of a Trainer with a Z-Power Ring, a Solganium Z, and its Z-Move, Searing Sunraze Smash.
In Securing the Future!, Lunala helped Necrozma by giving it some of its Z-Power. The attempt was successful in getting Necrozma to let go of Solgaleo, but it also angered Necrozma into attacking everyone again. After giving Gladion a Lunalium Z, Lunala and Gladion performed Menacing Moonraze Maelstrom while Ash and Solgaleo used Searing Sunraze Smash. The combined Z-Moves successfully gave Necrozma enough light to regain its true form and restore Poipole's home world back to normal. Afterwards, it, Solgaleo, and the Ultra Guardians went back to Alola.
Personality and characteristics
Lunala has a caring attitude towards humans, as evident in Full Moon and Many Arms!, where it saved Lillie, a girl it barely knew, from falling when she was knocked off her RideAltaria. Lunala is also playful, as evident by the way it was chasing Solgaleo through an Ultra Wormhole. After Necrozma took Solgaleo into Poipole's world in Full Moon and Many Arms!, in the next episode, Lunala fully recovered, but it rampaged around the Ultra Guardians headquarters, determined to rescue Solgaleo. This goes to show that Lunala seems to love Solgaleo, and is always willing to rescue it, no matter what it takes.
In Full Moon and Many Arms!, despite the best efforts of Tapu Koko and the Ultra Guardians, Necrozma was able to merge with Lunala and form Dawn Wings Necrozma. In this state, a special unit from Team Rocket attempted to catch it, but it was able to break through the net easily. Solgaleo then appeared and attacked Necrozma with Sunsteel Strike, forcing it to separate from Lunala. However, Necrozma then merged with Solgaleo to form Dusk Mane Necrozma, and left through another Ultra Wormhole.
In The Prism Between Light and Darkness!, the Ultra Guardians and Lunala followed Necrozma through an Ultra Wormhole and arrived at Poipole's home world. While Lunala went ahead to face Necrozma again, the Ultra Guardians stayed behind with Naganadel and were told of how Necrozma lost its light saving the world from a meteor. Afterwards, the Ultra Guardians found Lunala in the process of being defeated by Necrozma and rescued it. Intent on freeing Solgaleo and restoring Poipole's home world, Ash, Kiawe, Lana, and Gladion fired simultaneous Z-Moves at Necrozma, hoping that their Z-Power would restore Necrozma to its true self as the Blinding One.
In Securing the Future!, Necrozma absorbed the Z-Moves, but that wasn't enough to get it to let go of Solgaleo. However, with the combined Z-Power of the Ultra Guardians and their allies back in Alola, Necrozma was filled with enough light to release Solgaleo from its grasp. Despite their success, Necrozma was only angered by the attempt and attacked everyone so it could absorb Solgaleo once again. With the Z-Crystals they received from Solgaleo and Lunala, Ash and Gladion performed Searing Sunraze Smash and Menacing Moonraze Maelstrom, respectively. The two Z-Moves fully restored Necrozma back to its original self, Ultra Necrozma. Necrozma then used its power to restore Poipole's home world back to its previous state. Afterwards, Necrozma appeared in Alola before dissipating into light.
In the anime, the Aether Foundation, assuming that Necrozma is an Ultra Beast, gives it the codename UB Black (Japanese: ＵＢ:ＢＬＡＣＫUB: Black).
Personality and characteristics
In its weakened, black state, Necrozma was shown to be a highly aggressive Pokémon. It had a strong desire to absorb the light emitted by Lunala, determinedly chasing it all the way to Alola. It also took out anything that stood in its way, such as Solgaleo when it fought to protect Lunala. According to a legend regarding Necrozma, it was once a benevolent Pokémon that gave light to the Alola region along with the other members of the Light trio. This benevolent side was first seen in a flashback in The Prism Between Light and Darkness!, where it stopped a meteor from crashing into Poipole's world.
Upon being restored to its original form, Necrozma once again returned to being a benevolent being, using its regained power to restore Poipole's world back to its original lustrous, green state.