The Imperial Gate Divine Knife slashed right on Son of Heaven Yin's face, and the timing was impeccable. It was right when Qin Mu used Soul Guide to pull Son of Heaven Yin's soul.
Son of Heaven Yin received the blow head on, and the Imperial Gate Divine Knife nearly split him into half. The terrifying part about the knife wasn't only because of the power it had to be able to sever Earth Count's horn, but there was also another ability in which the divine knife could swallow primordial spirits.
Even Tian Shu, the knife bearer, could also have his primordial spirit swallowed when he was careless and got trapped inside for seven to eight million years.
The instant Son of Heaven Yin suffered from the attack, he could feel the world spinning, and his primordial spirit fell into the Imperial Gate Divine Knife.
'I've been tricked!'