For example, the Aether Law.
Having the ability to manipulate Aether had enable him to generate and manipulate Aether, the unique essence that flows through nearly all of existence.
If it is broken down, it is the source of Qi, Aura, and mana and the source of power for Quintessence which is Life Force manipulation.
Aether is the source of power for all of that ability.
However, Azief felt that if he fuses the Nether and Aether Law, he could then change the laws to Ethereal Laws manipulation.
And this is not some baseless feeling.
The moment when he tries to fuse the two Laws, an image enters his mind, that seems to reveal to him all the kinds of permutation and possibility that one could create when fusing the Laws
Ethereal manipulation is the ability to manipulate Ether, the essence that flows through all of existence.