who is that f*cking cat? (in the opening)
Edit: found the answer:
[…]drama cd 1 from DVD volume 1 explains the black cat
timeline 1 Madoka became a magical girl to save a dying cat that was hit by a car
however, she keeps this a secret from Mami, who would otherwise scold her for becoming a magical girl for such a “half hearted reason […]”
further reading:
http://kurogane.animeblogger.net/2011/04/26/madoka-magica-drama-cd-01/
Bonus: