Sky devils were terrifying, because they were invisible and traceless.
One didn’t know where they came from, or where they would go. They came like a gust of wind, and would also leave like a gust of wind. They were raised in one’s heart and came through the mind. They were not defendable, as everyone had weakness in the heart, through which, sky devils could drill in immediately, strike the primordial spirit and harm the foundation of the cultivation of Dao.
Walls could not stop sky devils; cities with strong defenses were just the same as flat areas in the eyes of sky devils. Countless layers of magic formations could deliver no effect to sky devils, and numerous seals were nothing to sky devils.