Question about Old One Souls

[Eldrisle]

I have never beat the game. I played until I got my first Old One Soul (The Iron King) on 360 but I just joined the PC Master Race so I had to start over. I eventually want to to use the Crypt Blacksword and a guide informed me that since I need to trade the Old Dead One's souls for it, I'll need to use a Bonfire Ascetic in the Black Gulch.
This leads me to the assumption that I need all four Old One Souls in my inventory in order to access the Shrine Of Winter and complete the playthrough. Am I even remotely close to knowing what I'm talking about? I just killed the Last Sinner and I'm wondering if I can consume her soul or if I need it.
I don't want to give off the impression that i start threads all willy-nilly. I've been searching and combing the boards I can't find the info anywhere.

[~Zarkith]

When you see text on the screen saying you've embraced a great soul, that's all you need. Whatever you do with the actual soul items are up to you and won't affect the shrine.

Slightly spoiler-ish tip: You don't embrace Freja's great soul when you kill her, you need to interact with the glowing spot at the edge of the cliff.

[Eldrisle]

Thanks :)

[Eldrisle]

So I don't need to kill The Rotten twice to get the Crypt Blacksword, riiiigh?

[Savrola-Games]

The old souls drop from NG+ onwards as well as the normal boss soul (which is the 'great soul' you need to open the shrine).

So it depends on what playthrough you are on. If you are just on NG, then yes, you have to get the area to NG+ to get the old soul, to get the weapon you want.

[Eldrisle]

Ohhh, weird. So the soul I need isn't actually dropped until I kill the boss in NG+?

[Cress's Lover]

in short, yes, you can consume the souls for weapons, souls and so forth and you still will be able to go into the shrine

[Cake for Mumm-Ra]

Yote, if you burn a bonfire ascetic at the second bonfire in Black Gultch, the Rotten will effectively be NG+. You don't need to beat the game first.