"Here's my condition," the man said, frowning as he pointed at Erik. "That power you've created is truly fascinating, and an advancement leap we weren't able to make in my time… but it's far too dangerous to leave in your soul. In its current state, it won't simply kill you if the bond somehow disappears, it's also a kill switch that this fairy can trigger any time she wants!"
He threw his arms up when he noticed Erik was about to react with anger. "Look! Let's not argue about whether or not she would, or what the chances are that your bond breaks for other reasons in the future. The point is that it's dangerous! We don't know how unstable this is! Let's say your soul is disturbed for reasons unrelated to your bond? How much does it take for this thing to rupture and kill you!?"
