Soul contracts were magic contracts specially used to store souls. They were very simple. Most demons that could use magic power could use them. But in fact, in the Abyss, soul contracts were rare because many demons did not have the habit of storing souls. The souls sealed in Fury's soul contract should be from her killing enemies and then sealing them inside over many years. Although the nephilim could also use souls, their demand was not as high as that of demons, so they could store them forever.
After putting away the soul contract, Roy laughed and asked Fury, "I guess you've verified the authenticity of the so-called Corruption power, right? Otherwise, you wouldn't have so easily concluded the deal with me. Am I right?"
"That's right!" Fury admitted readily. "Corruption power and the Void power you mentioned are indeed very similar and very dangerous. What I want to ask is, is there really no way to eliminate this power?"