Onbu

was an infant onbaa that was taken from its nest by a hawk and it was dropped on Naruto's back and thought he was its mother.

Appearance
Onbu is a ball-shaped creature covered in light brown fur. Only its ears and face were not completely covered. It had a tuft of fur coming from the top of its face covering its forehead. Onbu also had strings of hair sprouting from its face.

Pre-Shippūden Arcs
When a hawk came across Naruto Uzumaki, it became frightened and dropped the onbaa. It clung to Naruto's back for safety, mistaking him for its mother. Naruto does not notice its presence until it gropes Sakura. Despite his attempts to release it, the onbaa cannot be removed. Stuck with it, Naruto decides to name it "Onbu" because of the sound it makes. Onbu accompanies Naruto around the village, causing jealousy amongst his friends; Lee believes it to be some sort of training weight, while Hinata first confronts him hearing rumours that he has a kid, she faints upon seeing Onbu, when she wakes up and sees it again she faints again. Because of the time spent on Naruto's back, Onbu becomes obsessed with the red swirl on his shirt and will only eat fish cakes that have the same design. It can eat a seemingly limitless number of fish cakes.

Tsunade sends Naruto on a mission to clear a fortress of its bandit-occupants. The real reason he is sent on the mission is because Tsunade hopes it will dislodge Onbu. Onbu matures rapidly during the mission and, on Naruto's way home, has become an adult that towers over Naruto. It still remains attached to his back. Once they near Konoha, Naruto is attacked by Onbu's mother, trying to get her child back. This finally removes Onbu. Onbu then attacks Naruto too, but Naruto reminds it of all the fun they had together, prompting it to protect him from its mother. Onbu takes Naruto back to the village before leaving with its mother.

In the end, everyone except for Naruto has their own infant onbaa dropped on their backs by a flock of hawks in Konoha, while the latter laughs at their misfortune.

Trivia

 * Onbu's growth kept changing from scene to scene, at one point he was bigger and then he was smaller.

Onbu