After dreaming that he made a promise to the Legendary Pokémon Solgaleo and Lunala, Ash has a hard time waking up. On his way to school, he’s sidetracked by Tapu Koko, who guides him to a strange little Pokémon that looks like a cloud of stars. Lillie nicknames it Nebby, and Ash remembers his dream: he promised to take care of it!
This attracts the attention of Lillie’s mother, Lusamine, the head of the Aether Foundation. She and her colleagues come to meet Nebby and offer to take care of (and research) this unknown Pokémon. But Ash is resolute in his promise, so Nebby’s identity is a mystery for now!