Vol2 Ch7: Supporter
As Negary's 'Righteous', Noah was absorbed into Negary's body during the battle at the kiln of the first flame.
By the common conception that the True Spirit determined whether a person was themselves or not, then Noah was already dead the moment he was absorbed by Negary.
But in terms of personality, will, and memory, Noah was still living within Negary. After infusing himself with Soul's blood, Noah had already become a part of Negary, or perhaps to a certain extent, another personality of Negary.
What Negary had to do now was to install Noah's personality, will, memory, and emotions into the soul of this young man so that Noah's template would overwrite his, thus achieving the effect of reviving Noah.