Amachi

Amachi is a medical-nin/scientist, who was an accomplice of Orochimaru. He and Orochimaru terrorized the people of the Land of the Sea, and kidnapped the citizens for their deadly experiments (including Isaribi) which included making the ultimate underwater ninja for Orochimaru. He ordered Isaribi to attack ships, promising to return her to her normal form, but truly intending to dissect her once she was no longer of use. He also seemed to know Anko Mitarashi as well, since she was with Orochimaru at the time.

Much later, in the Sea Country arc, Yoroi Akado and Misumi Tsurugi joined him as bodyguards and assistants. He planned to steal gold from an arriving ship, and manipulated Isaribi into attacking it. It was also revealed that he planned on using his experiments to take revenge on Orochimaru. In the final confrontation with Anko, Naruto Uzumaki, Ino Yamanaka, and Shino Aburame, he also summoned the indestructible Umibozu, and later transformed into a Kaima. He was defeated by Naruto when he used the Nine-Tailed Demon Fox's chakra and was captured by Anko's team. Upon capture, he mentioned that he didn't know a way to cure Isaribi, and had planned to dissect her when she was no longer useful. Naruto grew infuriated and tried to strike him, but Anko held him back, only to slug Amachi herself.