A dozen or so White Dews and Snake Eye Berries entered Xia Fei's stomach. Using psychokinesis's Tier 4 technique Fearless earlier had consumed a great deal of Xia Fei's physical strength.
As his rank increased, Xia Fei felt the limits of the energy the White Dews could provide him more and more. It was as if this miraculous fruit was becoming less capable of meeting Xia Fei's energy needs.
Furball did not have the same problem. It took energy from Purple Hearts of Spirit. Purple Hearts of Spirit were exceptionally valuable, so they naturally had a better effect than the White Dews that Xia Fei ate.
Alas, the energy within the Spirit Hearts of Purple was too violent for Xia Fei. While the text he had taken from the Assassin Sect's secret chamber showed him a method for extracting energy from Hearts of Spirit, it required a complicated energy conversion device, which Xia Fei had never had the time or materials to construct.