A person's anima appears when channeling it through meditation laws as a resplendent glow exuded from the body with a shadow three feet above the head. After that the true fate comes out and fuses with the anima.
The anima also meditates and absorbs primal energy. This energy washes the body as a tiny maelstrom formed by the stomach. It absorbs the primal energy released by the anima and turns it into streams coming to one place.
While the worldly energy from the nine and chaos energy in the tenth all come from the heaven and earth, such that the cultivators there are restrained by this entity, this is not the case for Three Immortals, leading to the absence of tribulations. The cultivators here have their energy coming from the anima, not the world.
Furthermore, there is no difference in strength or cultivation speed between Three Immortals' cultivators and cultivators from other worlds up to the True Emperor rank. True Emperors are faster to reach the dao origin (mastering Anima) than a twelve will Grand Emperor.