The Heaven's Will Secret Laws (天命秘术) are the strongest techniques in the Nine Worlds, apart from the arts from the Nine Grand Heavenly Scriptures. Heaven's Will Secret Law allows one to communicate with the Heaven's Will, so its power is endless.
Every Immortal Emperor can create only one Heaven's Will Secret Law, and it is the highest achievement in their life. The power of Heaven's Will Secret Law is greatly exceeds other Immortal Emperor Merit Laws as it carry the Heaven's Will godly aura.
The Heaven's Will is different in every generation, so each Secret Law is also different and one of a kind. Because of that it is difficult to harmonize two different Heaven's Will Secret Laws inside one person, and yet, many geniuses throughout history were successful and cultivated two Heaven's Will Secret Laws at the same time.