In my fantasy WIP, the world I am making is a world where magic (in the form of ki/chi) exists but science (alchemy) is pretty big as well. Ki is very limited to humans, only very devout can gain access to it and that's after proving their submission to the will of the Gods. So with magic all but cut off to them, humans have turned to science to power themselves. My question is, how advanced should the science be? The world is Feudal Japan based with aspects of tribal Africa and the Caribbean mixed in. I have my main character run into several people who have used alchemy to give themselves abilities. I.E. he runs to into a guy who is all but invulnerable because of a potion he took that makes his bones as hard as metal. Is something like that too advanced? Or is it fine as long I explain it properly and consistent with it?