As far as we know, this might've actually how it went down
If you form a contract with me and become a Magical Girl, I can grant you a single wish.SFX: surpriseWhat did you wish for, Mami-san?That's your wish huh. What a cheap one.I would like to tell someone who has the leisure to think of a wish to think carefully before deciding.... call an ambulance ...Ah... I see...