"With Zhou Shu's strength, even if he has a weakness, we might not be able to deal with him," a Grotto-Heaven Master.
They were not inexperienced novices. As Grotto-Heaven Masters, they knew too well what kind of existence an expert of this realm was.
Not to mention Zhou Shu, even they didn't have too many weaknesses.
If they had any weakness, they might not have survived until now.
Which Grotto-Heaven Master didn't advance by stepping over a mountain of corpses and a sea of blood? They had countless enemies, and any weakness could put them at a disadvantage.
It was impossible for someone with obvious weaknesses to become a Grotto-Heaven Master.
Zhou Shu's strength was not inferior to theirs. How could such a person have a fatal weakness?