You are an average 14 year old girl living in Mitakihara City, turned Magical Girl through a contract with a mysterious creature named Kyubey. As you were hanging out with your friend and fellow Magical Girl, Mami Tomoe, you met Nagisa Momoe, a childish girl obsessed with cheese and a friend of Mami's.

Nagisa: ...Hey, uh, new girl, do you mind if we go to a convenience store and get some cheese? Mami says I can't go by myself and I don't have any money...