| Necrozma first appeared in Filling the Light with Darkness!, where it chased after Nebby and Lunala in an Ultra Wormhole. They emerged out of the Ultra Wormhole at the Altar of the Sunne, appearing before Ash, his classmates, Gladion, Lusamine, Wicke, Faba, and Professor Burnet.
It reappeared in Full Moon and Many Arms!, where, despite the best efforts of Tapu Koko and the Ultra Guardians, it 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. Nebby then appeared and attacked Necrozma with Sunsteel Strike, forcing it to separate from Lunala. However, Necrozma then merged with Nebby 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 Nebby 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 Nebby. However, with the combined Z-Power of the Ultra Guardians and their allies back in Alola, Necrozma was filled with enough light to release Nebby from its grasp. Despite their success, Necrozma was only angered by the attempt and attacked everyone so it could absorb Nebby once again. With the Z-Crystals they received from Nebby 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:ＢＬＡＣＫ UB: Black).
Necrozma's known moves are Prismatic Laser, Psycho Cut, and Metal Claw.