Serena is a young girl who lives in Vaniville Town when the protagonist moves into town. Serena is the main rival of the character, choosing the starter Pokémon which is super effective to the player's. She is also the character who teaches the player and Shauna how to catch a Pokémon, catching a Bunnelby with the use of her Fletchling. Soon after, she can be seen in Santalune Forest with the other friends.
Serena is the child of two prominent Pokémon battlers, and is seen as one of the two best battlers of the group of friends, alongside the protagonist.
Pokémon
Capture tutorial
Serena has another Pokémon besides her Fletchling, likely her starter, as noted by having two party slots filled during the tutorial.