As others have stated, you can "win" the game by holding down any of the two available keys.
How about having it so some daggers need to be hit from one direction, and other daggers need to be hit from the other? That'd make it more fun I think.
Anyway, minor complaint since I guess this is a mobile focused game, where I can see it being far more fun. Just add some background music and a bit more of variety and you'll have a pretty cool game. :)