Snowy

This Alolan Vulpix, nicknamed Shiron, is an -type Pokémon owned by Lillie. It is her first Pokémon.

As an egg
Vulpix, as an egg, was found by Principal Oak near Mount Lanakila. It was compared to a regular Vulpix egg brought to Alola from the Kanto region by Ash Ketchum. Oak took care of the Kanto Vulpix egg, and left the Alolan Vulpix egg in care of Lillie and the other students. Lillie decided to take the egg home to try and get over her fear of touching Pokémon, and after a wild Salandit tried to eat the egg, she managed to face her fear and held the egg to protect it.

Ever since then Lillie has been taking good care of the egg and fearing for its safety. The egg was later watched by Professor Kukui who was telling it to hurry up and hatch so it could play with the other Pokémon.

Later, the egg was in Lillie's care while the others competed in the race. During the race, she began to notice that the egg starting to glow. Mallow proposed Lillie should enter the race with it, after it hatches.

As Vulpix
The next day, the egg started to hatch. To everyone's discovery, Lillie named the egg "Shiron" while she was taking care of it. The egg cracked and hatched into a white Alolan Vulpix.

Trivia
Vulpix is the first Alolan Pokémon owned by a main character.