The Invincible Full-Moon System - Chapter 1071 Combat Awareness

... he gained a hint that ancient Awakened would not have assimilated with a spirit at the sixth-rank realm, the method of cultivating their own power was different compared to the new era.

Rex doesn't know when, but ancient Awakened assimilated with a spirit at a higher realm.

At the very least, at the seventh-rank realm or above.

Due to the burden of the mind, stressing over the preparation for this fight—he didn't realize he didn't realize that throughout their encounter, ...