When it was a Poipole, Naganadel is displayed as a curious and mischievous being. It likes to laugh at a lot of things. Much like how Ash's Goodra took an instant liking to Pikachu and admire his strength, Poipole instantly took a liking to Pikachu and admired his Electric-type moves. It also took a liking to Ash after he protected it from Team Rocket and showed it how Poké Balls work. After it was caught, it became fast friends to Ash's Alola team and his classmate's other Pokémon. Poipole also has a habit of spinning on its head whenever it is excited and would tend to hug Pikachu by nuzzling him. Poipole is also very playful to other Pokémon. For example, it intended on playing with an Alolan Exeggutor, which unintentionally causes it to send Ash rolling out from the Pokémon Center.
In spite of its overly mischievous and playful nature, Naganadel is very obedient to Ash and will instantly obeys Ash's instructions when he tells it to apologize for its deeds.
During a visit to Ula'ula Island for the preparation of Alolan Pokémon League Battle, Naganadel shows a serious side when it was surprised to notice Necrozma’s existence on Earth, upon looking at one of the books from Acerola’s library room. Thanks to Mina's teaching, Naganadel’s painting has been improved to foreshadow the incoming invasion of Necrozma to the rest of its friends.
It is very loyal towards its friends when it rescued Ash's Rowlet from being blown away in a sandstorm while traveling through the Haina Desert.
Naganadel began to show much more emotional moments, such as the tragic lifespans of Miniors, then eventually missing its leader, the older Naganadel and other Poipole. As shown when it was having a nightmare of its kind becoming endangered and scared within the dark Ultra Space, which is actually revealed to be its deserted home world due to the reason behind Necrozma’s downfall upon losing its light.
After evolving, Naganadel became stronger and more powerful than it was as a Poipole. In doing so, it developed a more heroic side of its personality like when it arrived back in Alola to save Ash, Pikachu and Kukui from Guzzlord.
Despite having evolved into Naganadel, its behavior still the same as its pre-evolved form. Ever since its fellow teammate, Melmetal, when it was a Meltan first participate the official Pokémon tournament with their trainer, Naganadel was also happy with its newfound fame.
Prior to its time with Ash, Poipole used to live in a peaceful homeworld where it lived with its fellow Poipole and was lead by an elderly Naganadel. The legendary Pokémon, Necrozma, who also resided in that world and was in its Ultra form at the time, gave Poipole's land so much light that it helped flourish all plant life everywhere. Since Necrozma provides light for all the plants, Necrozma became Poipole and Naganadel's sole protector. But then, one fateful day, a meteorite threatened to destroy Poipole's world as it plunges downward from space. Necrozma protected Poipole's world from the meteorite, but it caused it to lose its light and turn into its black form. Necrozma fell into a deep crevice and encased itself into a spiky and crystalized cocoon. Due to Necrozma's black form and lack of light, all of the plants began to wither and Poipole's world plunged into darkness. Poipole and Naganadel huddled into a cave where there are still remains of light left. But one of the Poipole decided to leave its home, hoping to find a better place to live.
Poipole was first seen where it was traveling through the Ultra Wormhole. Sooner or later, Poipole emerged from the wormhole in an unknown area and started to explore Alola. When Ash and the group serve as Ultra Guardians to capture Buzzwole, Poipole witnessed the battle and was astounded by Pikachu's Electric attacks. It was then seen playing around with Pikachu before leaving.
Later, Poipole was enjoying itself flying above the ocean during the night. While it was encountering a wild Chinchou, it recalled witnessing Ash's Pikachu using Thunderbolt attack on Buzzwole and decided to go looking for him, hoping to see Pikachu's electric moves again. Poipole went to the Pokémon School and while everyone was listening to Sophocles' lecture, it got Pikachu's attention and lured him out without anyone looking. Poipole shared an apple with Pikachu and began to show its affection for him. When Ash's Rowlet, who was sent to look for Pikachu, mistook Poipole's affections as if it was trying to hurt him, Poipole panicked when he dove down to attack it and used Toxic, which poisoned him. However, Poipole got scolded for what it did by Pikachu. Poipole apologized for what happened and assured Pikachu that it didn't know that Rowlet is one of his friends until now. Wanting to make things right with its new friends, Poipole offered to carry Rowlet and had Pikachu lead the way to the Pokémon school.While traveling through Hau'oli City, Poipole, Rowlet and Pikachu were attacked by Team Rocket as they wanted to capture them. Luckily, Poipole with its friends were saved when Torracat and Lycanroc arrived just in time to save them before the net caught them just as Ash showed up. Poipole was surprised and amazed that Ash saved them. After Bewear carries Team Rocket away from Pikachu's Thunderbolt, Poipole was taken to the Ultra Guardians base, where Lusamine analyzed the photos Rotom took, since it was unable to recognize it. Lusamine contacted the group and told them that she, Wicke, and Professor Burnet concluded that Poipole is, in fact, an Ultra Beast, which Team Rocket had already confirmed earlier. They also told them that they chose Poipole as a name it should be identified as. After Rotom updates Poipole's data, Lusamine suggested to have Ash take care of it until they could figure out the location of the wormhole it came out from. Ash made many attempts to catch Poipole with a box full of Beast Balls, but Poipole evaded all of them, thinking he was playing with it. Lillie suggested to have Ash demonstrate how going in and coming out of the Poké Ball works, which he did as he repeatedly sends out and recalls his Rowlet. After that, Poipole understood Ash's intentions and it went right into the last Beast Ball by itself, much to everyone’s surprise, as it wanted to be with him along with its newfound friends. At night, Poipole is shown playing with Ash and his Pokémon at Professor Kukui's house and painted a picture of Pikachu on the wall with its liquid.
Sometime later, Poipole traveled with Ash and Pikachu to the Hokulani Observatory on a class trip to learn about the lifecycle of Minior from Sophocles' cousin, Molayne. During the trip, they went outside to take a peak at the Minior shower near Starfall Hill. Poipole become fascinated by it due to the shimmering lights. However, Poipole discovered that one of the Minior didn't break out of its shell. So, Ash and Kiawe carried it back to the observatory. Poipole kept examining the Minior, until the next morning, the shell broke open to reveal an Orange Core Minior. Poipole tried to be friends with Minior, but it accidentally made it upset when it sprayed some of its liquid on it. Poipole realized its mistake and made it up by painting a picture of Minior on the wall with its liquid. Over the course of the day, Poipole and Minior had a wonderful time playing together and becoming friends. During the next night, another Minior shower came and Minior reunites with its kind. But as they start to float back up, they start to fade away into dust, since they can't live longer without its shell. The same fate happened to the Orange Core Minior, which made Poipole very sad. But it was comforted by Ash and Pikachu as they watch the Minior fade away. A few moments later, Poipole caught a glimpse of the legendary Pokémon, Rayquaza flying in the night sky.Later, Ash and Poipole encountered a trainer named Mina, who is painting pictures with her Ribombee. Mina reveals that Ribombee appears to have the ability to understand someone's emotions including Ultra Beasts. With Ribombee's help, Mina explained to Ash that the paintings Poipole makes is a way of Poipole expressing its emotions to others. She states that Poipole loves Ash and considers him, his classmates, their Pokémon, Professor Kukui, and Professor Burnett as its family. One night, Poipole had a nightmare that revolves in a place surrounded by darkness and filled with multiple sad Poipole as well as a dying Naganadel. The next day, Ash and his Pokémon began to notice Poipole feeling depressed and wondered what its problem is. So, Ash decides to find Mina and ask for her help. After defending Mina from Tupp, Rapp, and Zipp, she reveals to Ash and his classmates that Poipole is on a mysterious mission of some sort. Later that day, Poipole painted a picture that looks like Ultra Necrozma, which is a Pokémon Acerola mentioned back on Ula'ula Island and dubbed it as "The Blinding One."
At some point during the Alola crisis, Poipole, along with Naganadel and the rest of its kind, helped join everyone in sharing its light to restore Necrozma's original Ultra form. Afterwards, Poipole's homeworld flourished once again. But sadly, Naganadel informs Ash that Poipole wants to stay behind where it can protect its kind. Despite not taking this too well, Ash knew that Poipole had to stay for the best of its home world. He lets Poipole keep the Ultra Guardians tag to remind it of the times its been with Ash. As everyone departs back to Alola, Poipole drew one last picture of Ash and Pikachu before saying good-bye.
Sometime before the Manalo Conference, Poipole evolved into Naganadel. When Guzzlord and its two shiny counterpart partners in-crime invaded the main universe in Alola, Naganadel immediately rushes back to help its old friends, where it reunited with Ash and Pikachu. It seized Guzzlord with its newly-learned Thunderbolt attack. Together with Pikachu, Naganadel sent the Ultra Beast packing with their combined Gigavolt Havocs.After defeating Guzzlord, Nagandel officially rejoined Ash's team for his full battle in a exhibition match with Professor Kukui. Before his battle, Nagandel watched Ash's training with Melmetal, which it got dizzy by watching them spin around. During the exhibition match, Nagandel was used to battle Professor Kukui's Lucario. Before they began their battle, Naganadel was happily enjoying being part of exhibition match between its trainer Ash and his opponent Professor Kukui, as it was ready to go up against Lucario. During their battle, Naganadel was able to defeat Lucario before being recalled by its trainer. Ash later sent it back out to battle Tapu Koko, who had decided to join the battle as Kukui's final Pokémon.  Naganadel was managed to land some successful hits on the guardian deity, but was eventually defeated by Tapu Koko after several consecutive attacks. It was praised by Ash as he knew it battled hard before he continued his battle with Professor Kukui. 
After helping Ash win a successful exhibition battle, Naganadel sensed an Ultra Wormhole above Kukui's house. Ash, realizing that Naganadel had other Poipole in its world to look after, decided to let it go back and bids it one final good-bye. As a sign of their friendship, Ash had Pikachu use Thunderbolt for Naganadel to enjoy for the final time before it flew into the wormhole and disappeared. 
- Naganadel’s capture marks the first time Ash caught a genderless Pokémon, followed by Melmetal. Coincidentally, both are the currently known main evolved genderless Pokémon who even also uses Electric-type moves outside Pikachu.
- Naganadel is the first Ultra Beast owned by Ash.
- Naganadel is the only Pokémon Ash released that can still evolve, which is eventually proven to be true on its return.
- As a member of Ultra Guardian, despite being genderless, Naganadel wears a pendant that is commonly synchronized to be used by the confirmed male Pokémon members of Ultra Guardians, same goes for Melmetal, while Shaymin is a different case.
- Naganadel is also the first known expanded Pokémon of Ultra Guardian, who is not one of its original founding Pokémon, followed by Lana's Eevee, Shaymin and Melmetal.
- Naganadel is Ash's first Pokémon to evolve off-screen.
- Naganadel is the second of Ash's released Pokémon to rejoin him temporarily, first being Goodra.
- Coincidentally, they are both Dragon-type Pokémon.
- Naganadel marks Ash's first capture of a Poison-type Pokémon that he still owns since his Muk, 21 years apart from being captured.
- ^ SM089: The Prism Between Light and Darkness!
- ^ SM055: The Professors' New Adventure!
- ^ SM061: A Mission of Ultra Urgency!
- ^ SM067: Love at First Twirl!
- ^ SM069: Rise and Shine, Starship!
- ^ SM078: Twirling with a Bang!
- ^ SM085: The Long Vault Home!
- ^ SM079: Showering the World with Love!
- ^ SM084: The Shape of Love to Come!
- ^ SM090: Securing the Future!
- ^ SM140: Z-Move Showdown!
- ^ SM141: Exhibition Unmasked!
- ^ SM142: A Full Battle Bounty!
- ^ SM143: Fiery Surprises!
- ^ SM144: From Z to Shining Z!
- ^ SM145: Dreaming of the Sun and Moon!
At Oak's Lab
At Kukui's house
At Cerise Laboratory