Reaper Witch

Learning magic isn't easy.
Being told I'm some kind of rare reaper witch would be awesome except for the fact I can't use my magic unless I'm threatened. When I'm scared, my instincts kick in, but it's very clear I'm no hero. Heroes don't run from danger.
Yet, I do. Blame my parents. They taught me to be afraid of everything, even my own shadow. In this case, though, I might be justified. A great evil is trying to enter our world, and my blood is the key that unlocks a monster's prison.
Since I'd really prefer to not die, I'd better drag my courage out from deep-and I mean deep-within and learn to fight. The question being, will I learn how to wield my magic in time, or is the world doomed?