The divine power named Demon God of Great Black Heaven infused into Taishi Ci's body was returned after leaving the coverage of Fusang without being refined.
Nevertheless, as Taishi Ci was already among those closest to the breakthrough level, naturally, after receiving an inner qi equal to his own, he successfully entered another realm.
Although the power was returned after leaving Fusang, the insights remained, which is why Zhang Fei was astonished at Taishi Ci's achievement.
Similarly, Taishi Ci roughly understood why Xu Sheng, Mi Fang, and Cai Mao experienced fluctuations in the Inner Qi Manifestation stage.
In simple terms, it's the gap in foundational accumulation. If Taishi Ci's accumulation were sufficient, he could remain at the breakthrough level even after the external boost disappeared, but his foundation was lacking, so he fell back.
