Isobu (磯撫, Isobu), more commonly known as the Three-Tails (三尾, Sanbi), is one of the nine tailed beasts. It was last sealed within Yagura Karatachi of Kirigakure.
He was voiced by Chris Edgerly.
Isobu primarily resembles a large turtle, but with a crab-like shell, spikes all over its body, and three shrimp-like tails. Under its shell, it has red, muscle-like tissue. It has a pair of human-like arms and hands, but no hind-legs. His face is concealed between a large forehead and lower jaw — both of which have spikes. Its eyes are red and have crimson pupils. In the anime, the eyes are red with yellow pupils.
Its right eye is constantly closed. In the anime, Guren speculated this was because its eyes were the only soft parts of its body, being heavily-armoured, and thus kept one eye closed to cover more vulnerable spots. During the last remaining days of the Sage of Six Paths, Isobu was essentially much the same in appearance, albeit smaller in size with shorter spikes around its body, but was still many times larger than the Sage.
Isobu speaks in a timid manner, referring to itself as "boku" (ボク) which is usually used by young boys. Seeing that it had worked with Yagura, it's assumed that Isobu isn't as rude or outspoken as some of the other tailed beasts.