Madoka Magica: The Different Story Volume 2 (Manga)

Mami has joined with a new magical-girl partner in her efforts to rid the city of witches.  Miki Sayaka is a little green, but her swordsmanship is an undeniable asset to the cause.  But Sayaka brings more that her blade to battle: Her friend Madoka has joined the girls on their late-night missions.  Mami doesn't want to pressure Madoka into a decision about becoming a magical girl, but how long can Madoka remain on the sidelines as a passive witness when her friends are in danger?