What do you assume happens when you sell your soul? A one way ticket to hell? Well, yes. But the way you get there is infinitely more fun than you could ever imagine. Matthew sold his soul and now he has to finish his little revenge plot, see it through til the end. Whoever has hold of your soul, is then your master. Sure, maybe there is more of a hierarchy between demons, but who cares? You want something? Get it by any means necessary, your explanation means nothing to someone who already has fate planned out for you. You're simply following the plan, whether you know it or not.  A modern age Tower of Babel story, not very accurate to the source material, in a mix with a Faustian Bargain, again not very accurate to source material.  Fair Warning: This isn't a number based LitRPG or progression in any way. Sorry about that, but I'm not good with numbers. So instead the story is less about building up magic ability, in terms of stats?