|This article is about a/an ally in Kamen Rider Den-O.|
Mai is a little girl in 4th grade when she meets with Anna who tries to run away from Momotaros who she thinks is an evil pervert monster. Mai pretends to be be a karate 5th dan and tries to confront Momotaros, just realizing he looks monstruous. Mai succeeds to run away with Anna, where she gets the surname of Melon-chan. They also both learn that they're extremely similar. When arriving in front of their school, she realizes that Anna comes from 30 years in the future.
After Momotaros' quiz, Mai shows and gives Anna her "treasure", a Heisei New Era lottery winning bill. Shocker comes back in the Den-Liner and succeeds to take Mai in hostage. However, Momotaros possesses Anna and both transform into Kamen Rider Pretty Den-O to save Mai. After the battle against Ikadevil, they retrieve the bill however cut in half. They repair it with some adhesive tape, but Anna prefers giving it back to Mai, because Anna's real treasure is her friendship with her. Both girls greet each other when Anna had to go back to 2020.
Around 30 years after the battle against Ikadevil, Mai is now around 40 years old. When she asked her daughter Anna that before leaving the house she needed to tidy her room, as not done a previous time, Anna ran away. After a little while, she finds her daughter where she threw the lucky charm.
Behind the scenes
Mai is portrayed by Otoha (乙葉). As her younger self, she is protrayed by Tsugu Sasaki (佐々木 告 Sasaki Tsugu)