Decidueye first appeared as a Rowlet in The Delivery of Rotom and the Girl. Professor Kukui was seen testing Rowlet and Popplio's moves in his lab, causing a ruckus that sent all three flying through the roof and onto the beach, where they met Moon and Sun. While Sun introduced Moon to Kukui, Popplio sneezed, trapping Rowlet and Kukui in its water balloons. Though Moon immediately freed Kukui with one of her arrows, Popplio had to remind her to also rescue Rowlet. Due to spending so much time in the bubble, Rowlet developed a cold and had to be healed with Moon's medicine. Afterward, Rowlet took a liking to the girl, the two forming a bond because of their mutual preference of nighttime.
In The Decision and the Tournament of Six, Rowlet traveled with Moon to Iki Town, where a festival was being held. Later, he helped rescue Nebby from being attacked by a group of wild Spearow at Mahalo Trail. Due to the battle being three-on-one, Rowlet was unable to win, but managed to distract the Spearow long enough for Moon to get to Nebby.
In Going Ashore and Neighboring Akala Island, Rowlet was attacked by a pair of Team Skull Grunts as he was seeing Moon, Sun, and Kukui head off to Akala Island. By feeding him a Salac Berry she fired with her bow, Moon raised Rowlet's Speed enough to escape the Grunts and fly into Moon's arms. Afterward, Kukui noticed Rowlet liked Moon and suggested she keep him, which she accepted.
In Defeat and the Commander of the School of Fish, Rowlet was used to battle a Xurkitree that attacked Tapu Lele at Lush Jungle. Rowlet kept Xurkitree distracted long enough for Moon to shoot a Poké Ball-tipped arrow at it. Though Xurkitree escaped being captured, Tapu Lele was freed from its grasp, after which it angrily flew off. Afterward, Rowlet, the rest of Moon's team, and Mallow's Steenee helped find a Mirage Berry for Sun to give to Tapu Lele. By asking the local Pokémon of the area, Moon was able to quickly gather a large group of Berries and successfully find the one she was looking for.
In Truth and the Mastermind Behind Team Skull, Rowlet transported Moon to Po Town, where they clashed against the Ultra Beasts Guzma summoned to Alola. Rowlet was later used to try and stop a Nihilego from kidnapping Guzma. Their attempt was stopped by Xurkitree, which grabbed Moon, allowing Nihilego to drag Guzma into an Ultra Wormhole with it. Moon and Rowlet were rescued by Sun.
In Battle in Vast Poni Canyon, Rowlet was sent out alongside the rest of Moon's team to fight a group of Aether Foundation Employees at Vast Poni Canyon. They were later switched out for Anabel's team.
In Adventure in the Dark Dimension, Rowlet was revealed to have evolved into a Dartrix during Moon's time in Ultra Space. At the Ultra Megalopolis, Dartrix was used to help rescue Sun from an attacking Stakataka. By carrying her into the air, Dartrix allowed Moon to get close enough for Moon to shoot the Zygarde Cube in Sun's bag, releasing several Zygarde Cells everywhere. In Darkness!! The Mysterious Claws of Necrozma!, he was used alongside the rest of Moon and Sun's teams to assist Lunala against Necrozma, but was stopped by Lusamine's Naganadel.
After Moon exited Ultra Space, Dartrix and the rest of Moon's team were stolen by Faba and stored at Aether Paradise in Secret Lab B. In Regeneration!! The Power of the Sun and the Moon!, after Moon escaped Faba, she headed to Secret Lab B and found Dartrix and the others safe. While trying to prepare medicine for Gladion, Moon was ambushed by Aether Foundation Employees and had her team hold them off while she finished her work. While battling against a Huntail, Dartrix evolved into Decidueye.
When Moon arrived on Mount Lanakila in Finale!! The Battle Against the Other Dimension!, Decidueye used Spirit Shackle to stop Necrozma's movements while Solgaleo, Lunala, and Zygarde attacked it.