[He looked at it with interest, what a useful sort of talisman, to be able to reverse most anything. He would have to remember it for later.]

It's hard to say, since the nature is to sacrifice yourself to a spirit perhaps the reverse would be sacrificing a spirit for yourself?

[This ritual did require a trade after all.]

You sound like my old teacher. Maybe I hadn't thought about it too deeply at the time. I was trying to see what I could do.