Just need a little help. Basically, so far, Emil(protagonist) and Gwenyth(current enemy) who are brother and sister are prophecized ones. One is supposed to begin the end of the world, the others going to save it. Emil is thought to be the bad one.
That's the beginning, and the end is basically where they have a huge showdown, and Gwenyth wins, supposedly fulfilling the prophecy. Any help is much apprieciated.
I don't know if you've decided who starts the end of the world, so I'll write down ideas for each.
Protagonist: if the Emil starts the end of the world, he could (1) do it by accident (say, big explosion), and as time goes on, more "accidents" happen, and soon the world is in total chaos; or (2) he could see something is wrong with the world, something no one else understands, and knows that the only way to fix it is to end the world, so he does so.
Antagonist: if Gwenyth starts the end of the world, then maybe she (1) go on a killing spree just because she can't contain herself and Emil has to stop her; or (2) she feels neglected by Emil and starts doing bad things so she can get his attention.
I'm not sure if these helped, but I hope they can at least spark an idea.
Thanks!