The Akatsuki in Naruto have distinct appearances — be it Nagato‘s piercing-adorned face or Zetsu’s cactus-like visage and the ability to split in two. Keeping this frame of reference in mind, it is probably not that shocking for Kisame to look like a shark, but it’s still interesting to delve into the reasons why. It is important to note that the reason behind Kisame’s shark-like appearance has not been referenced directed in the anime or manga, hence any conclusions reached are merely speculative.
Kisame is a feared antagonist in the franchise, as he is also known as the Monster of the Hidden Mist, and hails from Hoshigaki Clan. Once a shinobi, he joined the Seven Ninja Swordsmen of the Mist, wherein he eventually went on to become an S-rank missing-nin while being partnered with Itachi. The two joined the Akatsuki later on, and have been often seen paired together during missions.
Kisame’s appearance could be a genetic trait
While the reason why Kisame has shark-like tendencies could be manifold, it could simply be explained by the fact that it is a genetic trait. This theory is further supported by the fact that a character named Shizuma Hoshigaki, a relative of Kisame’s, also possesses similar shark-like features. Shizuma does not appear in the Naruto manga but is a part of the anime-only arcs in Boruto. It is possible that the Hoshigaki clan carries a bloodline in which members possess shark-like attributes, especially keeping in mind that several bloodlines were purged in the Hidden Mist Village.
Alternatively, Kisame’s appearance could be a result of being a part of the Seven Swordsmen, whose members sport similar sharp, triangular teeth, cases in point being Chujuro, Zabuza, and Suigetsu. Moreover, the use of the sword, Samehada, could lend this appearance, as the weapon is sentient and scale-covered, which shaves off flesh instead of slashing it.
When Samehada absorbs chakra, the scales on the sword grow and reveal a mouth with several rows of shark-like teeth. When Kisame fuses with the Samehada, his appearance as a shark becomes more apparent, as he grows a tail and fins that appear quite menacing. This occurrence establishes a connection between the weapon and the user, and there could be some sort of hidden lore that justifies this similarity.
Interestingly, the creator of the Naruto manga series, Masashi Kishimoto, originally envisioned designing the Akatsuki members as entities with monstrous features, some looking like human-animal hybrids. Some of these ideas have been trickled down to the characters we know: Deidara has several mouths on his body, including his palms, while Sasori’s body is a puppet that can move erratically in order to strike enemies. Keeping this in mind, it makes sense for Kisame to look not entirely human, and his shark-like features could be a reference to the primal ferocity with which he engages in combat.
Whatever the reason behind Kisame’s shark body, he remains one of the most memorable characters in Naruto, mainly for his power and his use of strategy during fights.