Sylveon, also as an Eevee, has a huge passion and love for dancing, as she is seen to enjoy dancing her moves on a stage-like rock prior to her capture. She has been described as to be dancing on air by Serena. Eevee is also a very shy Pokémon due to her long time living alone in the forest. Whenever she meets new Pokémon or humans, she would tend to hide behind Serena or her friend, Bunnelby, revealed in A Frolicking Find in the Flowers! (her debut). Sylveon, as Eevee, slowly begins to open up about being around others as shown in Love Strikes! Eevee, Yikes! by letting Bonnie brush her fur. When battling, Eevee uses her dance moves to swiftly dodge her opponents. These dance moves are also used as a Sylveon.
In A Performance Pop Quiz!, Eevee has a fear of fireworks when Jessie as Jessilie performs in the Pokémon Showcase with her Gourgeist which made her ran away in fright. Her running away due to her fear of fireworks causes Ash and the others to look for her until they have some time to find her which Serena immediately found her after her hiding.
Since dancing with a trainer's Furret, Sylveon is no longer timid and now almost has full confidence in herself, though she still feels a bit nervous before performing in showcases. She has also began to interact with the other Pokémon, while maintaining her friendship with Bunnelby. With Clemont's Chespin, she was shown receiving encouragement from him and comforting him as a Sylveon even though she used to avoid him as an Eevee. With Ash's Pikachu, she showed concern and went to defend him when he was injured in battle as an Eevee. As a Sylveon she was shown cheering for him along with Pancham and Braixen. Lastly, she also interacted with Clemont's Dedenne, using her feelers to comfort it when bidding farewell.
Sylveon was first seen as an Eevee when she was spotted by Serena's Pancham and Clemont's Dedenne. She was dancing all by herself on a rock near a stream. Serena was impressed by her (Eevee's) performing skills and attempts to meet her. However, she discovered that Eevee is very shy among strangers. While she and her friends try to find Eevee, Serena's life was unexpectedly saved when Eevee called out to her to prevent her from falling down a cliff. In gratitude, Serena left a flower crown for Eevee to wear. The next day, Clemont attempted to lure Eevee with Serena's Poké Puffs. However, Eevee took it without Clemont noticing and made him believe that his Chespin ate it. Serena decided to perform in order to get Eevee to reveal herself to the group, which she successfully did. However, Team Rocket interrupted it by trying to capture her, Eevee. Serena and her Pokémon protected Eevee from them, but Eevee saved them and helped Ash's Pikachu blast Team Rocket off. After that, Eevee joined Serena's team and became her third Pokémon. However, it was immediately shown she has an affection to Bunnleby, possibly for allowing her to escape with the Poké Puff instead of Bunnleby calling over everyone and making Eevee uncomfortable.
Eevee was introduced to Shauna and Tierno. Shauna excitedly told Serena about the Eeveelutions, in which Serena took a liking to Glaceon while Eevee seemed to take a liking to Jolteon. Inside the Pokemon Center, Serena decided that Eevee should get over her shyness, so Ash, Clemont, and Bonnie sent out their other Pokemon to help Eevee feel more comfortable. Encouraged by Clemont's Bunnelby, Eevee brushed her tail over Dedenne, Frogadier and Pikachu. Chespin, whose accidental outburst scared Eevee, left her crying under her trainer immediately. Later, Serena and Shauna teamed up against Ash Ketchum and Tierno. Eevee was shy and hesitant to go battle at first, both as a result of still being shy and the stunt Chespin pulled off, but with the encouragement of the Pokemon and tapping her foot to Tierno's dancing, Eevee was soon able to dance quickly and confuse Blastoise, despite getting her paw temporarily injured in the process. She then used Swift on Blastoise. Seeing Eevee's dance moves, Serena got inspired. She called off the battle in order to practice them for her performance. Serena was then seen with Eevee, asking her to teach Serena and the team her beautiful dance moves, to which Eevee agrees.
At Anistar City, Eevee was scared of the amount of people at the Pokémon Showcase, so Clemont sent out his Bunnelby to calm her down. All was going well until the Free Performance, in which Eevee got scared of Jessie's performance's fireworks (despite being with Bunnelby), then getting scared by the amount of people there. Serena screamed for Eevee and desperately searched for her, but to no avail. Eevee, who was hiding under a bench as she possibly wanted to avoid being with other people, gathered all her strength to run to her trainer. Seeing that Eevee was safe, Serena delivered her performance, in which Braixen and Pancham utilized Eevee's dance moves. Eevee was dazzled after seeing the performance, sparking her interest at Showcases.
At the Pokémon Center in Anistar City, Eevee was admiring Serena's Princess Keys and assure her Trainer that she will give her all in the next Showcase. Eevee was put back into her Poké Ball when Serena, Clemont, Bonnie and Ash all head over to the Anistar Gym for Ash's Gym Battle.
Eevee was released to meet a Pokémon nicknamed Squishy, though it is currently unknown why she didn't freak out.
Eevee caught the interest of a wild Quilladin. She didn't love the Quilladin, and frequently used Protect and Double Team to get away from its acts of love. However, Eevee was soon drawn away by a lure along with Bunnelby, Dedenne, and Squishy by Team Rocket. Though thanks to Bunnelby, Eevee was soon reunited with her trainer. Quilladin, falling in love with a Flareon, bid Eevee farewell and ran to chase Flareon after Eevee rejected Quilladin's love one last time.
Eevee participated in her first Showcase at Couriway Town. Though nervous at first, she was quickly calmed down by Serena and her team which is both Pancham and Braixen. During the Theme Performance, Eevee was excited and happy that Serena and Pancham won. During the Free Performance, Eevee, Serena, and Braixen were able to charm the audience with their dance routine. While Eevee was dancing with Serena, she leapt into the air and landed on Braixen's branch. However, she got distracted by the crowd (as you'd expect) and fell off the branch. Eevee felt upset, but Serena encouraged Eevee to keep on dancing and sticking to the routine. Because of the mishap, Serena didn't win. Later, Eevee felt bad and even started crying because she blamed herself for the loss, but Serena told Eevee not to worry, and she raised Eevee up into the air, their bond growing closer.
Eevee was seen playing around with the other Pokemon in the flowerfields as Ash and the group are having a tea break. When Ash's Noibat screams due to being attacked and poisoned by the wild Breloom. Eevee and others are recalled back by Ash and the group.
Eevee is first being brushed by Serena as both Braixen and Pancham are arguing about who's next to be brush as Serena scolds them. After brushing, Serena and her friends were invited to a dance party hosted by Monsieur Pierre and the current Kalos Queen, Aria. Although Eevee wasn't sure about attending the party, but accepted the invitation when she partnered with Bunnelby. At the party, Eevee had a wonderful time dancing with Bunnelby and she happily danced with a trainer's Furret when everyone switched partners, despite the fact that you'd think Eevee would immediately run off screaming and crying due to being paired up with a stranger. After the dance, Ash and Serena were chosen to participate in a tag battle against James and Miette. Eevee partnered up with Ash's Pikachu and battled against Miette's Slurpuff and James' Inkay. During the battle, Eevee was severely damaged. However, when Serena gave Eevee some encouragement, she awakens as it forms a long single ribbon that sticks on Eevee's fur to cover Serena's hand and surprisingly evolved into Sylveon.
Sylveon manages to deflect Slurpuff's Energy Ball with her newly learned Fairy Wind despite Serena tells her to dodge, thus helping Ash and Serena win the battle in the process by defeating both Inkay and Slurpuff with Fairy Wind. Clemont also tells Serena that Sylveon is one of the, and also the most rare, Eeveelutions much to her surprise.
Sylveon was seen being brushed by Serena when Sawyer tries to ask Ash about Greninja's special form known as Ash-Greninja form which Ash was still unaware of its special ability.
Sylveon was released along with Braixen to team up with Ash's Pikachu, Greninja, Clemont's Chespin, Bunnelby and Luxray and Chapman's Chesnaught to attack a large boulder with their powerful abilities but was ineffective. However, they teamed up along with Ash and the group using a rope to pull the large boulder only to be interrupted by Team Rocket who binds everyone up just to capture both Pikachu and Chesnaught. When Robon sacrificed to save Chesnaught and being damaged by Team Rocket's Pokémon, Chesnaught was visibly angry for what they have done as he broke free from its bind and angrily hits them with Pin Missile to make Meowth dropped the remote to release them from being bound. Sylveon along with Pikachu, Braixen, Greninja, Chespin, Luxray and Chesnaught use their powerful abilities to blasts Team Rocket off for damaging Robon until Clemont repairs it in time. 
Sylveon lost a bit of confidence when she recalled the memory of losing her first performance with her friends as an Eevee before performing in the Fleurrh City Showcase. Luckily, her confident was restored again after Serena encouraged her by giving her a Poké Puff. Better than that, they won the Showcase. Nonetheless, she became worried when Palermo told them something serious.
Sylveon, along with Serena's other two Pokemon, arrived at Gloire City to participate in the Master Class Tournament. Serena dressed up Sylveon in her performance costume while backstage. When Serena and her Braixen performed and won the first round, Sylveon cheered along with Pancham. In the second round, Serena used Sylveon and Pancham. They were also able to advance to the semi-finals along with Jessie and Shauna.
Serena, using her Sylveon and other Pokémon in the semi-finals against both Shauna and Jessie. However, when Serena touches the floor and hurting her left wrist to make her fall, Sylveon uses her ribbons to strap her down to make her flip through the ground to end the performance. Serena manages to defeat both Shauna and Jessie in the semi-finals and to challenge Aria for the title of Kalos Queen. Before the battle against Aria, she, Pancham and Braixen became surprised to see Serena had swollen her left wrist during her performance in the semi-finals. During her performance against Aria, Sylveon used Fairy Wind and Swift to charm the audience. Despite having performed beautifully, Serena still lost to Aria. Palmero later gave Serena a card, telling her that she was willing to train Serena. Serena declined, wishing to finish her journey with Ash. Sylveon approved of her trainer's choice by smiling and waving her feelers, as she knew that she could continue to stay with her friend Bunnelby.
Sylveon alongside Braixen and Pancham are also helping Serena to put down Ash's high fever when he had gotten a flu after being washed up in the night during their heavy training. They were later confronted by Jimmy and his Pikachu who wants to challenge Ash in a Pokemon battle. Serena tries to tell him about Ash's condition but he did not listen who keeps speaking to his own rocker speech. Sylveon alongside Braixen and Pancham watch Serena to do battle against Jimmy while posing as Ash using Ash's Pikachu and Jimmy's. They cheered on Ash's Pikachu when he manages to knock Jimmy's with Iron Tail. As they continue to watch both Pikachus in battle, it was interrupted when both of them were caught from Team Rocket. She alongside Braixen and Pancham manage to deflect Jessie's Gourgeist's Shadow Ball with their powerful abilities allowing Greninja to release them both using Cut. After Team Rocket is blasted off, she and the others are impressed on Ash's recovery.
Sylveon was sent out of her Poké Ball with her friends to celebrate Ash getting all the way to the finals in the Kalos League. However, Sylveaon returned to her Poké Ball when Pancham and Chespin went missing.
When Team Flare began their assault on the Kalos region, Sylveon battled several Team Flare Grunts and their pack of Houndoom in order to buy some time for Mairin to retrieve Chespie from the Lysandre Labs.
However, the rescue mission was interrupted when Lysandre, the treacherous leader of Team Flare, activated the Giant Rock, absorbed Chespie, and formed into a destructive version of a Zygarde. The Giant Rock Zygarde started heading towards the Anistar City Sundial, which it intended on fusing with it so it will create an explosion that would destroy the planet and wipe off nearly every living being. While Ash and Alain rescue Chespie, Sylveon stays with Serena to help protect Bonnie and Marin from danger. When the attacking roots and the Giant Rock Zygarde coming close, Sylveon stand her ground with her teammates to protect Serena, Marin and Bonnie. After the Giant Rock Zygarde stooped and Chespie was successfully retrieved, Sylveon joins in the final battle against Team Flare.
After Team Flare's evil ambitions were finally put to an end, Sylveon, along with the rest of Serena's Pokémon, received Honor of Kalos medals for their heroic efforts against Team Flare. Sylveon helped Serena put on a performance to cheer everyone up due to everyone still feeling down from the incident from Team Flare. After Serena had a battle with Ash, Sylveon and Pancham were called out from their Poké Ball by Serena asking them both if they'll continue to grow with her which they agreed to do for her. Sylveon witness Serena call Palermo and tell her that she decided to turn down her offer to train with her but understood her choice. Through Palermo suggestion, Sylveon decided to accompany Serena to Hoenn to compete in Pokémon Contest over their.
In the end of XYZ, Sylveon bidded farewell to Bunnelby with teary eyes and comforted Chespin with her feelers. Then, along with Serena, Braixen and Pancham, they began their new journey in Hoenn.
- Serena's Sylveon, as a Eevee, was the second Eeveelution to be caught by a traveling companion of Ash's.
- Along with Serena's other two Pokémon, Sylveon enjoys a certain aspect of Pokémon Performing. In Sylveon's case, it's dancing.
- Sylveon has always had her injuries (as Eevee) for only 2 seconds before she forgets about them. She has had them all as Eevee on her paw (and in XY101, her adorable little face).
- Sylveon, as Eevee, would have been one of the fastest Pokémon in the anime. It is also possible that the Poké Puff used as an attempt to attract Sylveon, as Eevee, to the group and allow Serena to catch her was sweet.
- Sylveon is the first Eeveelution that belonged to a main character to evolve onscreen.
- Among Serena's team, Sylveon is the only one without an item.
- Braixen has her branch while Pancham has his sunglasses.
- Sylveon, as Eevee, didn't have the heart shaped tail tip like other female Eevee due to that not being implemented into the games at the time of her debut.
- ^ XY095: Love Strikes! Eevee, Yikes!, a wild Quilladin falls in love with Sylveon as an Eevee
- ^ XY089: A Frolicking Find in the Flowers!
- ^ XY090: Tag Team Battle Inspiration!
- ^ XY091: A Performance Pop Quiz!
- ^ XY092: Cloudy Fate, Bright Future!
- ^ XY094: From A to Z!
- ^ XY095: Love Strikes! Eevee, Yikes!
- ^ XY101: A Dancing Debut!
- ^ XY104: A Windswept Encounter!
- ^ XY105: Party Dancecapades!
- ^ XY106: A Meeting of Two Journeys!
- ^ XY108: A Watershed Moment!
- ^ XY109: Master Class Choices!
- ^ XY112: Master Class is in Session!
- ^ XY113: Performing a Pathway to the Future!
- ^ XY115: Battling at Full Volume!
- ^ XY129: Kalos League Passion with a Certain Flare!
- ^ XY134: The Right Hero for the Right Job!
- ^ XY135: Rocking Kalos Defenses!
- ^ XY136: Forming a More Perfect Union!
- ^ XY137: Battling with a Clean Slate!
- ^ XY138: The First Day of the Rest of Your Life!
- ^ XY140: Till We Compete Again!