This technique, developed by Amachi due to Orochimaru's initial interest in creating the ultimate underwater shinobi, drastically changes the user's appearance, giving them green scale-like skin, fins, and gills.
Isaribi was one of the earliest Land of the Sea villagers abducted for the experiments, and became the only known surviving prototype. Eventually, Orochimaru cancelled the project out of disinterest, but Amachi managed to finalise it against his sponsor's abandonment, applying the process onto himself.
The experiment left parts of Isaribi's body permanently scaled, and Amachi falsely promised that he can return her to normal, but later confessed that he had no cure for her, and instead plotted to dissect her once he was finished using her. Agents sent by Konohagakure believe that Tsunade will be able to reverse Isaribi's modifications.
The Kaima (海魔, Literally meaning: Ocean Demon) transformation can also change the user's eye colour, as seen in Amachi's case. This form gives them supreme fighting skills in the water, as they can move through the water much faster than normal, as well as giving them the ability to breathe underwater. Also the scales used in this form have a steel like quality that can stop a kunai. Amachi also demonstrates that he can shoot the scales as a weapon.
Amachi intended to use this technique's benefits to control the water routes of the world, which would restrict all the shipping businesses, effectively allowing Amachi to control the trading industries, similar to the functions of Gatō Company.