I like the idea but I'm not sure that it would see much play. For one thing, you have to be using King Ahab and have both him and the enhancement at the same time. Also, in today's meta, giving up a soul is not very common unless you're drawing and in T1 people don't typically have that much defense down anyways. Being that King Ahab is 7/7, he probably won't have initiative to even play it half the time and the other half it won't be that effective unless you're facing a deck that mostly balanced which usually have a protect fort or are N.T. I'd imagine that it would be used even less in multi-player due to the fact that it won't be your turn when you play it and getting rid of defense could allow your other opponents to just walk in for free souls, even after getting one from you. I could see it being potentially used in T2, but even more so protect forts or N.T. defenses are used. If anything I think this card is a little under-powered and could use a boost. I'd suggest either adding a way to win the battle but give them a choice of 'insteading' or at least making it cbn or an interrupt since you'd be losing the battle anyway so you might as well gain from it.
Also, as Drrek said, you'd have to discard your own ECs unless you splashed it in a N.T. offense which I wouldn't foresee happening.