Kaiman is the lead character of the manga. He appears to be the victim of a magic user, who laid a curse on his head.
Other than that, he has no recollection of his previous life. He has the head of a large reptile, with no other alternates in limbs or body. There are cross-shaped marks over each of his eyes.
It appears that despite having his head chopped off, he can regenerate it in a matter of time.