Time travel sucks. No accurate time travel story ends happily, even if the resolution overall is good. Looper is a great example of a good one. I think Primer too, but I still have trouble with it, even with all the aids and charts. Oh, and 12 Monkeys, an easier one to follow.

who's power is to go back in time

Also stopping time. And hammerspace. Like, for storing whole aircraft carriers, if she felt like it. Also teleportation. Also creating projectiles out of thin air (but I think that goes for most magical girls in the series). Possibly also flight, or just jumping very high, but again that probably goes for all of them.