I'm just going to come out and say that I don't like those ideas, but it's yours and the GM's decision whether you want... that kind of character. 

Keep in mind, of course, that the real world in Madoka is actually quite futuristic, and that relatively young cultural sensations such as Rock may not actually be relevant in such a setting. Although, in one scene Madoka's mom IS seen playing an air guitar (if I remember correctly), so I may be wrong on this.

Actually, that brings up the question, is this taking place in Mitakihara City?