I edit that last part, I couldn't remember if it took a number of hits for him to be affected my A level statistically but I look it up on the wiki:

[b]The ability requires that Berserker must be killed by A rank attacks twelve times, once for each of the labors, before he can be defeated. He can only be killed by someone with an A rank strength statistic, A rank magecraft, or an A rank Noble Phantasm[/b]