Primordial Technique
Many means of growing stronger quickly existed across the universe, but only a few were truly efficient for the individual. No matter how similar their anatomy may seem, everyone had different characteristics, physical properties, and attunements.
Michael, for example, had a powerful physique with naturally high energy absorption and annexation rate, further augmented by the Sacred Constitution and his perfect High Ascension. He also had fewer impurities than others. To be precise, he was on the brink of perfectly purifying his body.