Sovereign Immortal Fetus Gu

Sovereign Immortal Fetus Gu is the rank-nine human path Gu produced by Spectral Soul Demon Venerable's plan at Yi Tian Mountain. Shadow Sect gathers the Ten Extreme Physiques and immense resources to refine it as a way to create an otherworldly body unconstrained by ordinary conflicting dao marks. (Chapters 1018–1020 and 2301)

Consumption and consequence

The Gu is consumable rather than a permanent worm retained inside an aperture. Fang Yuan takes and uses it at the moment of refinement, transforming into the sovereign immortal body and leaving Ying Wu Xie and Shadow Sect to recover a plan meant for Spectral Soul. (Chapters 1018–1021)

The resulting sovereign immortal aperture can cultivate multiple paths without the usual dao-mark interference, but the body brings its own maintenance needs and exposes Fang Yuan to Shadow Sect's pursuit. Later explanations identify human path as the Gu's foundation while noting heaven path profundity in the body and aperture it creates. (Chapters 1079, 1368, and 2301)