Rotom Pokédex/Manga

The Rotom Pokédex debuted in The Grand Entrance and Delivery Boy Sun. Originally, it was a regular Rotom that Professor Kukui requested to receive from a region outside of Alola so that he may use it to fuse with one of his Pokédexes. Due to this particular Rotom having a weak body, it was unable to be transferred electronically, so was given the task of delivering Rotom to Professor Kukui while also using her pharmaceutical skills to keep it healthy along the way.

After Moon successfully delivered Rotom, Professor Kukui decided to have it enter 's empty Pokédex. Due to Sun's mishandling of the Pokédex, Rotom refused to enter it and ran away in disgust. Angered by this, Professor Kukui forced Sun to retrieve Rotom while he attempted to clean the dirty Pokédex.

Later, it was revealed that Professor Kukui had a spare Pokédex, which he gave to Moon. This Pokédex was the one that Rotom decided to enter, becoming the Rotom Pokédex in the process.

Moon later traveled to Lush Jungle with Mallow to find a Mirage Berry. There, they found in battle with a. Not knowing anything about the Ultra Beast, Rotom went up to Xurkitree to try and record data on it. Xurkitree retaliated by shooting Rotom with a powerful Electric attack, forcing it to fall to the ground and shut down. When Rotom later reactivated itself, it could only utter one word: "".

While traveling from Akala Island to Ula'ula Island, Professor Kukui's yacht was attacked by a wild. Though Sun managed to defeat the Pokémon, he, Lillie, and Rotom ended up separated from Moon and the others. When doing his second trial at the site of the former Thrifty Megamart, Sun was given the task of taking a photo of the Totem Pokémon that lived inside. Shortly after entering the area, Sun and Lillie were attacked by the Totem Pokémon, a, which destroyed the camera Acerola gave him for the trial. While Sun had battle Mimikyu, Rotom revealed itself and let Sun use its Poké Finder function to replace the broken camera.

As the battle went on, Rotom translated Mimikyu's speech to reveal that it was angry at Sun for insulting its ragged appearance, as other humans had did in the past. After encouraging Mimikyu to find companions who would appreciate it despite how it looked, Sun added Mimikyu to his team and gave it the nickname Franc. Rotom took a picture of Sun and Franc together and emailed it to Acerola, successfully completing the trial. Afterward, Sun thanked Rotom for his help and suggested it join his team, which Rotom rejected.

By the time Moon arrived in Ultra Space, Rotom had rejoined her. Using the powers of the Pokédex, it was able to sense a, who would be able to take them all back to their world. Upon finding it, they discovered the Ultra Recon Squad members Zossie and Dulse riding it.