It's voluntary. Istredd would swear up and down that when they snuggle down on this makeshift bed together, he'd do just about anything in exchange. Besides, he truly doesn't think of this fight as a Lucifer mess. Nero is who overreacted. Most people can hear something vaguely insulting and move on with their life.

"It was definitely all a test of some kind. I didn't give them anything physical of mine." Istredd is far too used to potions and magic to do that. He is suspicious as soon as those requests are made. He doesn't blame them though. They were clearly in research mode, trying to understand these strangers they allowed in their midst. He suspects all of their reasoning is solid, but it means they're currently the specimens.

Did you visit the tree? Something about it ... reminded me of the Singularity.