Why does Kisame look weird?
This strange look could be related to the clan kisame belonged to, about which no one knows though. This could be due to the creator wanting to add some difference . Kisame is a water style user so maybe the creator just wanted to emphasize it. Theres no official reason to support this look of Kisame.
Why does Kisame look like?
Kisame has the ability to fuse with Samehada: Samehada performs the same function as a tailed beast, constantly flooding Kisame’s chakra network with stored chakra. Moreover, Samehada is a sentient, separate being from Kisame: Which makes Samehada a viable tailed-beast substitute.
Is Kisame a mutant?
Throughout the Naruto series, some of us might suspect that the only shark-man in the series is Kisame only, maybe at some point, he underwent a weird mutation that changed his appearance. But in the Boruto anime series, it showed that he’s not alone.