Miya is a Himedere. Meaning she is a person that wants to be treated like royalty. She is spoiled, obsessive, possesive, and has a major crush on Makoto Kashino. Though she make act rude and full of herself, she is actually a very supportive, and confident person. She uses her good traits for her own benefit (The reason she was supportive of Ichigo's team winning, is because she wanted revenge for her loss).
Cake Grand Prix (Middle School Division)
Miya Koshiro lead the team called Team Koshiro and defeated her opponent. Won against Team Ichigo. 'Lost in being a good person and continues to want to marry Makoto Kashino .
Main Cake Grand Prix Tournament
Lost to Team Tennouji.
World Cake Grand Prix
During the World Cake Grand Prix, she bought the Andorra campus of St. Marie. During the first competition, she makes frozen fruit cups which isn't popular at first because of the weather and is losing to the opposite team. She orders the workers from "Château Seika" to come to buy her fruits which helps her win the competition.