ok, I have an idea... Because of your darkness powers being unstable, I think "a piece of the shadow" will help you out (The cloak my character wears he calls "the shadow" due to the vengence he put in it seemed to create a life of it's own) - in terms of stabilising and giving you more control of your powers. Now, whether you want to reveal your dark powers or not won't matter, as if you don't, it'll be more or less a memento, where "I'll be in the battle with you" (due to the vengeful spirit created in the cloak is none other than Jakob's own vengence, so he's in the cloak, more or less)
yeaah, a little confusing, but if you can understand me, think it over...