Lewis was given a Pokémon Egg as a prize for winning the Battle Royal Tournament in Conclusion of a Royal Bout!
A few episodes later, in Breaking the Ice!, the Egg hatched into a Vulpix. After getting to know Lewis, Mars, Luna and Lillie, as well as their Pokémon, Vulpix was captured by Lewis.
Vulpix remained rather unused by Lewis in battle, due to her inexperience. He did, however, use her in his Lush Jungle trial battle against the Totem Lurantis in It's a Jungle in There! Vulpix revealed its Ability to be Snow Warning, although the hailstorm it created quickly petered out. Despite fighting bravely, Vulpix was quickly taken out by a Petal Blizzard.
After training with Lewis and a wild Castform in Weather You Like it or Not!, Vulpix learned to use her Snow Warning Ability properly. This came in handy during Lewis' rematch against the Totem Lurantis. Vulpix was Lewis' final Pokémon and utilised Snow Warning to ensure Lurantis kept taking damage, as well as slowing down its usage of Solar Blade. After trading several blows with Lurantis, Vulpix finally managed to take it down with Powder Snow, resulting in her first ever win.
Lewis later used Vulpix as his first Pokémon in his Grand Trial battle against Olivia in A Rock Solid Grand Trial! She battled against Olivia's Nosepass and managed to hit a few times with Powder Snow, freezing it in the process. However, Nosepass quickly thawed itself out and struck Vulpix with Stone Edge, although she held her ground. Lewis then had Vulpix freeze the ground with Powder Snow, allowing her to move quicker around the battlefield and restricting Nosepass' movements. Vulpix then began attacking Nosepass from different angles with Powder Snow, eventually taking it out with Feint Attack. Vulpix showed signs of fatigue after all the intense battling, causing Lewis to retire her for the remainder of the battle.
Vulpix was used alongside the rest of Lewis' Pokémon to battle Novu's Rusted Pokémon army, using Powder Snow to freeze the advancing army.
In Clash on the Cape!, Vulpix was sent out to battle Hau's Steenee. Despite the type advantage, Vulpix was defeated by a powerful Double Slap. She was also Lewis' first Pokémon in his battle against the Totem Vikavolt in The Sound of Success! Vulpix used Powder Snow to slow down Vikavolt's movements and managed to hit it with Feint Attack, although she couldn't stand up to its Wild Charge and was defeated.
Vulpix was later used by Lewis to battle a wild Turtonator in Setting the Trap! During the battle, her Powder Snow collided with Turtonator's Flamethrower. As Flamethrower began to push through the Powder Snow, Vulpix suddenly learned Ice Beam, breaking through the Flamethrower and hitting Turtonator in the hole on its stomach. Turtonator then countered with Payback, followed by Flamethrower, defeating Vulpix, though giving Lewis an idea on how to defeat Turtonator.
In Aplenny of Discoveries!, Lewis sent out Vulpix to help him find some treasure in the cave systems on Isle Aplenny. While searching, Lewis discovered an Ice Stone, which he learnt from Mars could evolve Vulpix into Ninetales. Vulpix expressed an interest in evolving, but before she could touch the stone, it was stolen by a wild Boldore, who had been hording treasures from the competitors. Vulpix battled Boldore and knocked it back into its treasure pile with Feint Attack, causing the Ice Stone to fall at her feet. With Lewis' encouragement, Vulpix touched the Ice Stone and evolved into Ninetales. Ninetales then proceeded to defeat Boldore with her newly-learned Moonblast and returned the other competitor's treasures. While the pair didn't end up winning the competition, Lewis and Ninetales decided they were happier that she had evolved.
Due to her recently hatching from her Egg, Vulpix displays many childlike qualities, such as being very energetic and playful and often gets tired very easily, especially in battle.
Vulpix is shown to enjoy battling, although she initially would get upset whenever she loses and has to be encouraged by Lewis - this is likely due to her still being relatively young. Recently, however, Vulpix has been shown to be completely fine after losing, signifying a growth in her maturity. Her need for encouragement from her Trainer was also seen in Aplenny of Discoveries!, as she seemed to ask Lewis for permission before evolving.
Upon evolving, Ninetales lost her childlike personality and became a calm and friendly Pokémon. Ninetales also proved herself to be a rather adept battler, being easily able to defeat a Boldore despite a type disadvantage.