Aiko is a girl one year older than Shin'ichirō who attends a different school than he does. She is going out with his friend Miyokichi Nobuse, but instead has feelings for Shin'ichirō. Aiko continuously tries to get closer with Shin'ichirō, such as asking him to go shopping with her instead of Miyokichi, and when she goes out with Miyokichi, she does not have the same vigor as when she is just with Shin'ichirō. Aiko has known Shin'ichirō since they were kids, and was introduced to Miyokichi through Shin'ichirō. She helps out at her family's Imagawayaki shop named Imagawayaki Ai-chan. She is shorter than Shin'ichirō, and enjoys teasing him from time to time.