Mizunoto (癸, Mizunoto) is a member of Konohagakure's disbanded Anbu faction: Root.
In the anime, to prevent Hiruzen from being reinstated as Hokage, Danzō gave Mizunoto and nine other Root members a mission to assassinate him. Disguised as a foreign shinobi, he fought the Anbu accompanying his target, who turned out to be a disguised Kakashi, resulting in the mission's failure.
Like all other Root Anbu, Mizunoto is unwaveringly loyal to Danzō. He also looks out for his best interest, voicing concern that all the citizens of Konoha would die leading Danzō's goal of becoming Hokage pointless.
Mizunoto is a tall shinobi, with black hair tied in an elaborate top-knot. He wears a typical Anbu cloak. His mask is unusual in that it has two colours in it, with dark teal, dot-shaped eyebrows, and a red, sharp-toothed mouth.
As an Anbu, Mizunoto is a presumably a powerful shinobi. He also wields a sword which indicates him being skilled in kenjutsu. Danzō had enough faith to assign him and nine others to assassinate Hiruzen, and though this ended in failure, Mizunoto managed to survive in a battle against the famed Kakashi.
When Pain attacked Konoha, Danzō instructed Mizunoto and the rest of the Root Anbu to not assist the village until the chaos died down. Mizunoto, however, questioned Danzō's instructions saying that it would be pointless if he were to become Hokage if all of Konoha's citizens were dead. Danzō responded that most of the villagers will be safe and that it was all for Tsunade's era to end.
As ordered, he and the other Anbu remained underground while the battle ensured. 
- "Mizunoto" (癸) is the tenth sign of the Chinese calendar.
- Mizunoto's name was only divulged in a Studio Pierrot Settei of Root members.
- During his début in the anime, he was depicted with brown shaggy hair and again in episode 197. His appearance was corrected in the Kakashi Anbu Arc with his entire attire including his coat and mask being changed to match his manga appearance.
- His mask is used in Naruto Shippūden: Ultimate Ninja Storm Revolution as a customisation item for characters.