Hidden effect of the skill Blood Manipulation?
Taking into consideration that Bai Zemin had to not only kill a total of 20,000 enemies with specific characteristics and besides that consume an astronomical total of 6 First Order Soul Stones, the amount of resources and time needed to fulfill the requirements needed to evolve the Unranked skill Unstoppable Front Charge to the First Order skill Shadow Blink could be considered colossal.
To begin with, while it seemed easy, the two requirements where Bai Zemin needed to kill 10,000 Agility-type enemies and 10,000 enemies with high jumping ability were not easy at all. Sure, killing such beings might not be crazy depending on the overall strength difference, however, finding that number of those specific types of enemies would definitely not be a simple task considering that the Soul Record had only just reached Earth a little over a month and a week ago.