That secret to breaking through to the Sky Opening Realm, the one exchangeable with military merit, should have been this.
The so-called earth, water, fire, and wind did not mean they had to be Subordinate Rules among those four Primary Rules of earth, water, fire, and wind. Four kinds of Subordinate Rules that matched the Traits of earth, water, fire, and wind would do.
This secret to breaking through to the Sky Opening Realm was, in truth, just a layer of window paper.
For those who did not know, trying to guess it on their own would make it very hard to guess correctly. After all, how to verify it was itself a huge problem.
Among the human race's Emperor Lord Inheritances that Chen Fei had seen, there were many ideas regarding how to break through to the Sky Opening Realm, but in the end, none had the ability to prove whether those ideas were true or false.
Controlling one Primary Rule and breaking through to the Sky Opening Realm—among the human race's inheritances, this speculation was the most common, but this path was also almost the most impossible to complete.
In the Black Stone Domain, controlling two Subordinate Rules already made one an extremely powerful Dao Fusion Realm Peak.
Across the long history of the human race, Emperor Lords who controlled three Subordinate Rules were as rare as phoenix feathers and qilin horns. Moreover, those three Subordinate Rules all belonged to branches within different Primary Rules.
Among the human race's Emperor Lords, the most anyone had controlled under the same Primary Rule was two Subordinate Rules. As for a Subordinate Rule under a third Primary Rule, there was simply no way to continue.
When comprehending them, it was especially difficult, as if the Subordinate Rules under a Primary Rule