the guide on the site says you don't need it but I followed the guide and did till I got the key and tried to do eva's quest but when I got all the way there I couldn't click on the bottle. All I could do was read the paper on the wall. I went back and redid everything again to the point I would have received the key then tried again and still the same result. I finally finished the Charlotte quest and got the ma stone (or whatever that black stone necklace thing is) and went to try eva 1 more time and the battle worked. That's why I'm pretty sure you need the stone.