Quote Originally Posted by Aralith View Post
Now, about the Stagnant Lifestream, I cannot say. DoC didn't give us many clues about it's origin, use, or how it is controlled. It obviously has something to do with Vincent, considering that Lucrecia was studying it as part of her research on her thesis on Chaos, which she later applied to Vincent. We also know that Nero has some control over it. How or why we do not yet know. How the Stagnant Lifestream applies to and effects Vincent is not yet known. Perhaps it is just a mystery where we must suspend our disbelief, or perhaps it will be explained later on, but just because it didn't exist in the original game, doesn't mean that it's inconsisten with it. There's a difference.
Chaos was a being completely made of Stagnant Lifestream. Vincent has it inside of him, this is why he was immune to Nero's darkness. After Chaos "die" in the end of the game, Vincent don't have any connection with SL anymore.

And if i remember well, Nero was injected with SL when he was in the womb(like Sephiroth and Jenova). After he was born, he accidentaly absorbed/killed his mother with his darkness. This is explained in DoC Online.