"I will gain data about how your soul interacts with chaos energy and the changes it undergoes in your struggle with it. I won't get access to your thoughts or anything. And any information I acquire cannot be used against you as a realm lord. The monitoring will end once you die or if you manage to beat chaos energy back."
It was a tempting offer. Legion-3 suspected that the realm lord the law of will be getting a lot of advantage if he gives his permission. So he overcame his fear of the realm lord to ask for more.
He knows the realm lord can't outright kill him but that doesn't mean he has the right to offend such a terrifying person. It is not a wise action to do at all. It was with this caution that he asked for the two most important things to him.
"I want you to rescue my Original body and give me something that can help with this chaos energy."