Nijihara Ink is a normal girl who goes to a normal high school. She excels at academic studies but isn't so good when it comes to sports. However, her biggest issue is that she possesses an underdeveloped body and is often mistaken for a grade schooler. Even those who know otherwise have a tendency to treat her as a kid. One day, Ink meets a talking duck. Ink takes "Ark-kun" home and discovers that he is, in fact, a powerful magician cursed into the form of a duck. Ark-kun then convinces Ink to become a Magical Girl in order to help others. Thus begins the adventures of Pastel Ink! Just what does Ark-kun expect to get out of this arrangement?