It is entirely possible to play the game without ever picking up this item. It simply makes combat easier.
This item leaves the player's inventory should a new playthrough begin.
It is possible that the corpse where this item is found is that of Caryll. However, it makes no sense why Caryll would wear the Yharnam Hunter Set. Therefore, it seems more plausible that a hunter from the original workshop might have found it somehow and was caught with it.