As a wild Pokémon
Ash, Clemont, and Bonnie first encountered Dedenne in A Battle of Aerial Mobility during their journey to Santalune City. Bonnie was eager to care for the cute Pokémon, and asked Clemont if he would catch him for her to allow her to raise and take with her when she was old enough to be a Pokémon Trainer. Clemont agreed, and Ash helped her; however, Dedenne ran off crying when a Fletchling stole the berry he had harvested from the tree. After the same Fletchling was caught by Ash, Dedenne was last seen watching the group as they left.
Soon after, in A Shockingly Cheeky Friendship!, Dedenne reappeared to the group and stole some food, prompting the gang to give chase. This resulted in Pikachu getting lost alongside Dedenne. The two became friends, and managed to save each other from Team Rocket. After reuniting with the group and defeating Team Rocket, Clemont caught Dedenne and then allowed him out of his Poké Ball so he could stay with Bonnie in her satchel.
With Clemont and Bonnie
In An Appetite for Battle!, Bonnie used him in a battle against Clemont's Chespin. Due to Chespin being overweight at the time, it tripped during its attack, falling near Dedenne where a single Thunder Shock defeated the Grass type, giving him and Bonnie the win.
In A Jolting Switcheroo!, while the group was resting at a Pokémon Center, Lyn took Bonnie's bag, mistaking it for her own since the two bags looked so similar. Since he was resting inside earlier, Dedenne was accidentally taken by Lyn and her older sister Lena. When he woke up, he accompanied Lyn while she tried to find her Pichu. Lyn also gave him a red ribbon, which was used for identification when she lost Dedenne. When Clemont used his "Radiowave Amplification Device" to amplify Pikachu's energy waves, Dedenne found them and began to follow them to a vineyard where they were both attacked by Beedrill. Though he fought off one of the Beedrill with Thunder Shock, he was attacked by several more. Eventually, he was saved by Pikachu and reunited with Bonnie. He later had dinner with Ash, his friends, Lyn and Lena but he was not hungry as he was given lots of snacks by Lyn during the day.
In One for the Goomy!, Dedenne tried to be friendly to Ash's Goomy, but it was afraid of Dedenne as Goomy, a Dragon-type, was weak against Fairy-type Pokémon. Team Rocket showed up and attempted to capture everyone's Pokémon, and were attacked by startled Lotad and Lombre, and Dedenne was separated along with Goomy, Pancham, Serena, and Bonnie. Dedenne tried to give Goomy leaves on the way to help regain its energy but it was still scared. Later when Serena was battling Team Rocket with Pancham, he used Nuzzle on Pancham after he got confused and, under Bonnie's command, teamed up with Pancham to defeat Team Rocket. Afterwards he followed Goomy's slimy trail after it ran away, due to the battle reminding it how its original home was destroyed by Bug-type and Poison-type Pokémon. He traveled through a small hole to reach Goomy, who was about to be captured by Team Rocket. He battled them again, but was almost defeated until Goomy, who saw that Dedenne was trying to help it, used Rain Dance, distracting them long enough for Ash and friends to find them, leading to Team Rocket being defeated once more. Overcoming its fear of Dedenne, Goomy affectionately nibbled on Dedenne's ear, which made Dedenne happy.
Despite officially belonging to Clemont, in The Future Is Now, Thanks to Determination!, Dedenne stayed with Bonnie when Clemont left for Lumiose City by himself.
In A Diamond in the Rough!, Ash and the gang reunited with Goodra at the wetlands. Dedenne was shown to be very excited, as he was the first one to reach Goodra. Later, when Team Rocket trapped six Carbink in one of their cages used to capture Pokémon and was discussing over what to do with them, Dedenne, who was eavesdropping, attempted to free them. He first tried nibbling on the corners of the cage, and when that didn't work, he used Nuzzle in attempt to break the cage. Not only did that not work, but the ruckus also attracted the attention of Team Rocket. Team Rocket promptly sent out their Pokémon to chase Dedenne away. Dedenne ran right into Bonnie, who was looking for Dedenne, and upon seeing Team Rocket's Pokémon chasing Dedenne, she ran away and followed Dedenne back to the group. With this, Team Rocket began attacking the wetlands with their Carbink mecha. After defeating Team Rocket and retreating to relax in a cavern pool, Dedenne was shown happily diving off Goodra's head and into the water.
In Battling With a Clean Slate!, Dedenne and the rest of Clemont's Pokémon received medals from Professor Sycamore for their heroic efforts against Team Flare.
In Till We Compete Again!, Dedenne noticed Bonnie feeling sad, since the group would soon go on their separate ways. At the airport, while everyone said their goodbyes, Dedenne became upset and ran off. He was eventually located by Pikachu, who used his electricity to track him down, and was comforted by Bonnie. Afterwards, Dedenne bade farewell to Ash, Pikachu, and Serena.
Bonnie taking care of Dedenne
Dedenne's habit of sleeping
It was made clear in his very first appearance that Dedenne is a gluttonous Pokémon. In A Battle of Aerial Mobility!, his desire for a berry was strong enough that he was willing to fight Pikachu over it, and he only approached Bonnie because she had the berry in her hand. He reappeared to the group in A Shockingly Cheeky Friendship! to steal food. Dedenne is also a bit timid, as shown in his debut when he got upset when Fletchling swooped in and ate the berry Bonnie had for it. In A Shockingly Cheeky Friendship!, although initially unresponsive to her, Dedenne becomes very close to Bonnie, as he is often seen in either her hair or satchel. Dedenne is also prone to sleep while he is conserving his electrical energy, although he does so at the most inconvenient times, such as when he slept during attacks by Team Rocket in Grooming Furfrou! and Mega-Mega Meowth Madness!. However, Dedenne has been shown to be a competent battler when he is focused, and has no problem taking commands from either his Trainer or carer. Dedenne can sometimes be an affectionate Pokémon as shown in A Shockingly Cheeky Friendship! and Going For the Gold!, when Bonnie nuzzles Dedenne, she causes him to use Nuzzle, giving Bonnie a shock. In Bonnie for the Defense! and One for the Goomy!, he has been shown to be affectionate to others as well.
Dedenne has special relationships with a few specific Pokémon. In particular, he has a sibling-like relationship with Ash's Pikachu, looking up to and respecting him. The two of them often communicate using the electrical energy from their cheeks, such as in One for the Goomy!. Ever since that episode, Dedenne has also had a remarkably strong friendship with Ash's Goodra. Although the latter was frightened of Dedenne at first, they became friends once Goodra, as a Goomy, realized how much Dedenne cared about it and was willing to go to any lengths to keep it from harm. Their bond was also shown in Good Friends, Great Training!, when Dedenne gave Sliggoo a hug after they were reunited, Defending the Homeland!, when Goodra shared its food with Dedenne, Beyond the Rainbow!, when the two of them had to say goodbye to each other, and A Diamond in the Rough!, where the two reunited after Goodra's long absence.