Magic Day

All people born on a specific date in some world have magic/a power, and only those people. Because of some truly horrific things magic/the power has done (some deliberate, but most due to untrained magic/power), all magic users are sent to one or more ghettos/internment camps/concentration camps (if multiple, some are worse than others), from birth- I'd assume they'd remove the non-Magic Day kids born in the camps, too. There are, obviously, people who try to keep their kids from being taken away (and when they're successful for a while the kids don't get their magic under control, leading to more incidents, and exposure of the kid), and a lot of worry when the birthdate's supposed to be anywhere near Magic Day.

So eventually there's a kid who's born nowhere near Magic Day- not the direct opposite day of the calendar, either, just some random day- who has magic. When he's really young it's always subtle things. When he gets old enough to understand about magic he's terrified of it and wants nothing to do with it. Maybe he goes to the authorities to turn himself in, but gets laughed at because he wasn't born on Magic Day. He clamps down on the magic, not using it at all, until eventually he has to for some very important reason, then trains it in secret. And of course he eventually uses it in public and everybody's horrified at it even though he saved lives. In the end, he somehow frees the magicians and gets a more tolerant system put in place- preferably not through a show of force.

All ideas are free for the taking.