Naganadel first appeared in Poipole's dream where it dying from the lack of light. It reappeared physically where the Ultra Guardians arrived in Poipole's homeworld with Lunala during a mission to save Nebby. After being healed from dying, Naganadel telepathically told the Ultra Guardians that the being they call UB: Black is actually the fallen Blinding One Necrozma itself. Naganadel revealed to them that Necrozma once provide light for their world and flourished everything. But one day, a meteorite threatened to destroy their world. Necrozma unleashed its power and protected Naganadel and its pack, but the meteor caused it to lose its light and it fell into a deep crevice. Necrozma went into a long slumber and because of its lack of light, Naganadel's homeworld turned dark and became a barren wasteland. Naganadel searched everywhere to find a new place for its kind to live, but it got old and weak. Then, many years later, the Poipole that is owned by Ash Ketchum, left Naganadel and the pack in hopes of finding a better place.
Later, when Ash and the gang are trying to free Nebby, Naganadel and its kind helped join everyone in sharing its light to restore Necrozma's original Ultra form. After successfully freeing Nebby and restoring Necrozma's Ultra form, Necrozma used its powers to replenish Naganadel's world and its vegetation. Before the Ultra Guardians and the Legendary Pokémon depart for Alola, Naganadel informed Ash that Poipole wants to remain with its kind and protect its home from future threats. Although Ash did not take it really well, he knew it was for the best. He lets Poipole keep the Ultra Guardians tag as a reminder of the good times Poipole had with him and his classmates. As everyone leaves, Poipole drew one last picture of Ash and Pikachu before saying good-bye.
Despite Poipole finished its task, it can still return to Alola, sometime after it evolved into a Naganadel off-screen.
None of Naganadel's moves are known.