"Devil's Trade"
But aside from giving soul immunity to a soul that was traded away in a deal, Jake's trading ability even had more functions that seemed to be against the sky.
The deal didn't always have to be fair, as long as both parties really 'consented' to the deal. Jake had to give some kind of token as a symbol when making the deal and he had to abide by the deal itself.
Otherwise, he would also die.
However, this ability gave Jake various other inspirations, and Jake found out that people could even give away their abilities to him, as long as the deal was sealed.
Of course, many people would not make such a deal that involved giving away their abilities, but many low-level ability users with useless abilities would be interested in giving away their secondary abilities that were useless in exchange for something from Jake.