Amachi

is a medical-nin and scientist who was an accomplice of Orochimaru.

Background
He and Orochimaru terrorised 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 that time.

Abilities
Being a medical-nin, Amachi uses a scalpel as a tool and has good chakra control in general. Due to experiments on himself, he can transform into a fish-man hybrid. While in this hybrid form, he can use water nature techniques such as spitting a strong stream of water from his mouth. His movements are improved greatly due to his transformation and he is also able to breathe underwater. He can summon a sentient mass of water that takes a powerful Fire Release technique to defeat.

Land of the Sea Arc
Much later, Yoroi Akadō 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, who cancelled the underwater ninja project due to lost of interest.

In the final confrontation with Anko, Naruto Uzumaki, Ino Yamanaka, and Shino Aburame, he also transformed into a complete Kaima Form and summoned the indestructible Umibōzu. He was defeated by Naruto when he used the Nine-Tailed Demon Fox's chakra and was captured by Anko. Upon his 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 after asking him about Orochimaru's whereabouts.