Plan F (Part 2)
The closer Nalrond's bodies got to merge into one, the denser they became.
To manipulate his cores and protect his bodies, Lith and Quylla had to keep double the impurities of a regular bright blue core which meant that Nalrond's odds of survival would be zero the moment the merging process reached completion.
They exploited Nalrond's vigorous mana flow, Invigoration, and the temporary malleable state of his bodies to get rid of everything that wasn't necessary to keep nudging his evolution in the right direction.
It would have been an impossible task without the Eyes marking the dangerous impurities, the Hands harnessing the power of the mana geyser to finely regulate the speed of the Awakening process, and the Mouths allowing for a negligible cast time.
Nalrond's nature as a true mage gave him years of experience with fusion magic so the moment his mana started to flow and the vortexes to appear, he knew what he had to do.