Yang Gu

Yang Gu is the counterpart needed to reverse the bodily transformation caused when Bai Ning Bing uses Yin Gu during the explosion of the Northern Dark Ice Soul Physique. Fang Yuan retains it after the rebirth, making its promised return the central leverage in their early alliance. (Chapters 199–200)

Leverage and later custody

The Gu can change Bai Ning Bing's transformed female body back while lowering the recovering extreme aptitude. Because her physique tends toward one hundred percent again, the explanation presents Yang Gu as part of a repeated control method rather than a permanent cure for the underlying pressure. (Chapter 199)

Bai Ning Bing expects Fang Yuan to break his promise but travels with him because he controls the only established route back. Their conflict over Yang Gu persists through Southern Border. Much later, Ying Wu Xie produces a Yang Gu to restrain her killing intent, but its disposition after that scene is not firmly established. (Chapters 227, 260, 381, and 1248)