If Kaidou has been surviving without a devil fruit then he truly is hax, but given by his name "hundred beast" he may have one, he may have the mythological zoan fruit, or a level above that? The only hundred beast I know is the hectatoncles from Greek mythology. Kaidou seems to be rather brash though, we don't know the full extent of his abilities because when shanks confronted him and
came back to marinefold he didn't have any noticeable scratches. Is it weird that whenever I see Kaidou I think he looks like Fugitora, it's weird, to me they look alike, facial wise