Answer:
I am a box that holds keys without locks, yet they can unlock your soul.
I am the tool, for inspiring many. Buy me in the store, for not much more than a penny. Don't overuse me, or my usefulness will go.
I cut through evil like a double edged sword, and chaos flees at my approach. Balance I single-handedly upraise, through battles fought with heart and mind, instead of with my gaze.
I have one eye. See near and far. I hold the moments you treasure and the things that make you weep.
What binds two people yet touches only one?
You use it between your head and your toes, the more it works the thinner it grows.
Difficult
Animal
Easy
Food
Funny
Kids
Logic
What am I?