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 if they begin a new playthrough.
Cut description of the item: "Enables etching Caryll's runes into one's consciousness".
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.