Alex created the most pure Azure Dragon's bloodline he could from the tons of blood he had collected. Just as with the Black Tortoise's bloodline, this too would be more akin to the bloodline of the progenitor's children, rather than the progenitor himself.
Still, there wasn't much else Alex could do. After all, the only way for him to get the Progenitor's true bloodline was to get it from the Ancestral Blood Pool, and it was more or less obvious that he would have no way of getting to it.
The only one who could be given a chance would be Pearl, but if he went there, he would likely be forced to undergo an evolution session, which would most likely kill him as the Azure Dragon progenitor would have no way of dealing with Pearl's very unique soul.
Since he was done with the blood now, he had to start taking it.
