I hope you found it cause I'm a bit late with the answer and feel free to tell me if I'm wrong because I dont really remember but I'm pretty sure it had to do with using the 4 remembrances on the table and then ascending your soul twice, gaining the item "Soul of Elsbeth Krähenlied" or something
Pretty sure you get a non missable soul item that's equippable in the early game, before some boss. Then late game after getting the first 4 remembrances you can find an altar that lets you ascend your soul. you need to find two of these and ascend twice.
Think thats it. Ending isnt much just a new picture and a line of text.
Good luck!