Later, to test his theory, Huo Hai deliberately turned back and walked toward the outside for a long time before finally finding a Spirit King realm wraith. He killed it casually, immediately picked up its mental power crystal, and began experimenting.
"It seems only a difference in major realms produces a noticeable difference in effect." After examining the results, Huo Hai gained some understanding of these mental power crystals. A Spirit Emperor realm mental power crystal could restore his depleted mental power within a day. How long that recovery effect lasted depended on its owner's strength in life; the weakest could not even sustain it for a full day.
The strongest, however, could sustain that recovery effect for several days. But a Spirit King realm crystal core restored his mental power noticeably more slowly. After testing it, Huo Hai found that it would take more than ten days to replenish his mental power.
Most importantly, even a crystal from the peak Spirit King realm could last only an hour or two. Such things might be very useful to Spirit Emperors and Spirit Kings, but they had little effect on a Spirit Emperor like him.
It seemed Spirit Emperor realm soul crystals still worked best. Helpless, Huo Hai turned back again and headed deeper inside. He wondered just how much a Spirit Emperor realm crystal would benefit him if he could obtain one.
As he advanced, Huo Hai spared none of the wraiths he encountered, and the mental power crystals in his inner space gradually piled up. At this point, another question occurred to him. According to what he had heard, the mental power crystals in the Nether Soul Grotto had negligible effects on anyone above Seventh-Level Spirit Emperor. It seemed these resources would be useful to him only until he