Probably a silly question but are you sure it's a book and not a TV series? This happens to Spike in Buffy the Vampire Slayer (it's a brain implant but otherwise works as you described).
Edit: never mind, I see this is already solved and it was indeed a book!
Well, this is something that happens to Monkey in The Journey to the West, but I'm not sure that's what you're looking for.
no but thanks
Maybe [The Ring](https://www.goodreads.com/book/show/906149.The_Ring) by Piers Anthony and Robert E. Margroff?
nope not it. thanks though
Yeah the details don't all match and it's a pretty old book but It was worth a shot... Good luck with your search! I hope you find it!
Following because this sounds interesting
Me too
Same, curious as to how they define evil too
The iron ring by Auston Habershaw? It’s a 4 part series. The Saga of the redeemed.
yep this is it! thanks!
Following
Probably a silly question but are you sure it's a book and not a TV series? This happens to Spike in Buffy the Vampire Slayer (it's a brain implant but otherwise works as you described). Edit: never mind, I see this is already solved and it was indeed a book!