Puella Magi Madoka Magica

Madoka Kaname has a dream of a girl fighting something terrible above a burning city, and a small white animal at her shoulder asking her to make it stop. The next morning the girl from the dream — Akemi Homura — transfers into her class and tells her, calmly, to please not become a magical girl. Madoka and her friend Sayaka meet the white animal anyway. Kyubey offers any wish in exchange for the contract. The series is what the contract actually means, what the girls who signed it before her went through, and how many of them Homura is willing to outlive trying to break the cycle.