• English / United States: Aya
• Japanese / Japan: アヤ
• Japanese (Romanized) / Japan: Aya
• Japanese (Trans) / Japan: Aya

Aya is the younger sister of Koga and she trains in Pokemon Jujitsu at a Dojo located in the Johto Region. Ash and his friends first encountered her, she was training with her brother in a large old Japanese styled mansion that also serves as the Fuchsia City Gym. Aya's Venonat had been leading Ash Ketchum and his friends through the building until they finally encountered Aya. Aya threw a bunch of shuriken at Ash Ketchum and pinned him to the door. She told Ash Ketchum that it was his fault for letting his guard down and challenged him to a Pokémon match with me or he wouldn't be able to get out of the mansion. Like most girls that Brock encountered on his journey, he found Aya attractive and complemented her on her pink suit. Like her brother, Aya's personality is a bit stiff as she seems to spend too much time training.

Battle against Ash's Bulbasaur at the Fuchsia City Gym

The battle was a 1-on-1 battle and Aya's Venonat was sent out to battle against Ash's Bulbasaur. Aya's Venonat tried to use Stun Spore on Ash's Bulbasaur to get an advantage in the battle but Ash's Bulbasaur was able to blow it away from itself. Ash's Bulbasaur then used Leech Seed on Aya's Venonat which ended up to be too much for it as it sucked out all of Aya's Venonat power and forced her to recall it.

Koga and Aya were both impressed with Misty's Psyduck and Aya wanted to trade her Kongpang for it. Misty though realized her Psyduck was more powerful than she had initially thought and decided that she wouldn't trade with either of them. After his loss to Ash Ketchum, Koga realized that he was still far lacking in experience and he and his sister continued their training at the mansion.