Onbaa


 * Name: Onbaa or "Onbu" in the case of the infant on Naruto's back
 * Voice Actor: Kari Wahlgren (young Onbaa), Lex Lang (adult Onbaa)

Onbaa is an cat/sloth/bear/monkey-like animal who Jiraiya had encountered during his journey as a child, then wrote a story about it. Tsunade thought it was a lie until she saw the creature. A newborn Onbaa is abducted by a hawk that Naruto Uzumaki scares, causing it to drop the newborn Onbaa on Naruto's back. Having mistaken Naruto for his mother, it clings to his back and cannot be removed.

It first became known to Naruto when its little arms ended up grabbing Sakura Haruno's breasts. She attacked Naruto in retaliation until she realized that Naruto doesn't have arms growing out of his armpits. Kiba Inuzuka attempted to remove it. At Tsunade's office, she made a reference to Jiraiya having encountered an Onbaa. It even frightened Shizune.

The village then learns of the Onbaa as Rock Lee considers Naruto competing with him and Hinata Hyūga keeps fainting at the sight of it. Naruto names the creature after the sound it makes which is "Onbu". Onbu becomes obsessed with the red swirl on Naruto's back and will only eat fish cakes that bear a red swirl similar to Naruto's.

Naruto is forced to leave the village for a mission to attack some bandits that Tsunade ordered him to attack. During the time, the Onbaa on Naruto's back slowly matures. On the way back to the village Naruto is attacked by Onbu's enraged mother who mistakes Naruto for Onbu's kidnapper.

When separated from Naruto's back, Onbu matures into a violent adult that attempts to kill Naruto. After being reminded of Naruto, Onbu blocks his mother's deathblow to Naruto. Onbu, himself, carries an unconscious Naruto back to the village. Before traveling out of sight, Naruto wishes Onbu luck with his mother.

Soon after Onbu leaves the village, the entire population of Konohagakure is mistaken as the mothers of countless infant Onbaas dropped into the village by hawks. Tsunade begs Naruto to tell her how he removed Onbu from his back. Naruto joked that she should have a sumo match with it like Jiraiya did, thus angering her even further.

Trivia

 * Onbaa is the species name, Onbu is the name Naruto gave the infant creature.