The life of a Spirit Cultivator is not infinite.
But beyond the White Flame Level, the length of life ceases to have boundaries. Time, to them, no longer holds any meaning. Maybe they will die, but they don't know when.
At that realm, death comes either by being killed, committing suicide, or following destiny, naturally closing their eyes, awaiting the end of life.
So Ning Shiqi, he too doesn't know when he will die. He has been living all this while, and he doesn't know why.
Perhaps it's because he feels he is the last of the Ning Clan, and his existence represents the existence of the Ning Clan. But with only him left, what meaning does his existence hold? He doesn't know, nor has he ever figured it out.
Maybe it's just because he couldn't figure it out, that he has been living aimlessly, in a fog.
Letting time slip away, numb.
His heart has become as calm as dead water, no longer capable of stirring any ripples.
