Miki

Miki is a character of the day who appeared in Hot Matches! (EP154).

Miki had been training her Skarmory in the mountains between Azalea Town and Goldenrod City for several weeks prior to meeting Ash and his friends. She defeated many Trainers, but was very eager to battle Fire-type Pokémon in the hopes of teaching her Skarmory how to overcome its type disadvantage. Brock found Miki to be very pretty, but Miki mistook him as a Trainer and challenged him, telling him to use a Fire-type. Skarmory successfully defeated Brock's Vulpix and later Ash's Cyndaquil. However, Ash believed that Cyndaquil could become stronger than Skarmory if it could light its flame when needed. Over dinner, Miki revealed that she follows an intense training schedule; Ash went on to adapt it to help his Cyndaquil become stronger and finally control its flame.

Miki decided to have a rematch against Ash to see how well his training had progressed, and Cyndaquil proved to be powerful enough to defeat Skarmory. Miki complimented Ash on his training, and she was inspired to go on her own journey and take on the Johto League Gym Leaders.

(Source: Bulbapedia)