Berserker

The answer is that, it is a result of both the resilience of his body, as well as his techniques. God Hand has the ability to make Berserker's body immune against an attack after it has been damaged once by the said attack. Also, Berserker himself possesses the skill to see through an attack he has witnessed before. However, due to Mad Enhancement, this "technique of a swordsman" is sealed. As a result, he can only count on the ability of God Hand.