From Bulbapedia, the community-driven Pokémon encyclopedia.
Aya (Japanese: アヤ Aya) is a ninja and a Pokémon Trainer who specializes in Poison-type Pokémon. She is the younger sister of Koga, the Fuchsia City Gym Leader, and is a student of the Gym. Apparently, she was raised by Koga since she was young. She also has interest in poetry.
In the anime
Aya debuted in The Ninja Poké-Showdown, where she encountered Ash, Misty, and Brock in the Fuchsia Gym. Aya challenged Ash to a battle with her Venonat and Ash agreed—sending out Bulbasaur. He won the match easily with his Bulbasaur's Leech Seed. After the battle her older brother Koga appeared.
Aya reappeared in Ariados, Amigos, where she was training at the Pokémon Jujitsu Academy, learning Pokémon Jujitsu. She and her Venonat were unable to master it; she even faced Ash and his Bulbasaur in a rematch and lost. But after an encounter with Team Rocket, she was able to bring out her Venonat's full potential and defeat them. She then returned to the dojo to fully master Pokémon Jujitsu.
Aya is set on becoming a ninja warrior, thus she trains and studies intensely to fulfill that goal. Her time at the Pokémon Jujitsu Academy has taught her to turn her weaknesses into her strengths, and she relies on her Venonat's status moves to overcome tough opponents.
This listing is of Aya's known Pokémon in the anime:
| While trying to find their way through the Fuchsia Gym, Ash and his friends encountered Aya, who challenged Ash to a battle. During the battle, Aya used Venonat against Ash's Bulbasaur. Eventually, Bulbasaur was able to defeat Venonat with its Leech Seed. Aya also tried to use Venonat to battle against Team Rocket, but was tied up by a sticky net cast by James and Jessie.
Venonat reappeared in Ash's flashback in Bad to the Bone, when he remembered how he obtained his Gym Badges.
In Ariados, Amigos Aya used Venonat in a rematch against Ash, who used Bulbasaur again. Like before, Venonat lost the battle. It was also later used to battle and defeat Team Rocket who had stolen Poké Balls from the dojo.
Venonat's known moves are Stun Spore, Psybeam, Poison Sting*, Tackle, Supersonic, and Rest.
|| The Ninja Poké-Showdown
| Voice actors
|| Rikako Aikawa
|| Rachael Lillis
In the manga
Aya and Koga in The Electric Tale of Pikachu
In The Electric Tale of Pikachu manga
Aya makes a cameo appearance in Pikachu's Excellent Adventure.
Jessie, James and Meowth get trapped in Koga's Gym while searching for the Hidden Village with Ash's Pikachu, a Charmander, a Squirtle, a Kangaskhan and Tommy. She appears in the background during Team Rocket's battle with Koga. Their battle is only shown briefly in a montage sequence and it is unknown whether Team Rocket was victorious or not. It is also never shown if Ash himself battles Koga or Aya.