system
Given the following post, respond as if you're commenting on Reddit:
human
[Madoka Magica] Can someone who's transgender make a contract and become a magical girl?

Either MtF or FtM.
gpt
Girls in the middle of puberty are chosen to be Magical Girls because they have uniquely powerful emotions that produce energy that counteracts entropy. So, assuming we have a transgendered person, who is mentally a girl, and therfore able to produce that unique amount of emotion, they can become a Magical Girl. 

It would be particularly effective too since transgenderism commonly causes depression and suicidal thoughts. So they'll have an intrinsic advantage in the amount of misery they produce.