Onbu

In its infancy Onbu is little more than a round puff of light brown fur with green eyes, its ears and face the only parts left bare, a tuft hanging over its forehead and loose strands sprouting from its cheeks. As it shoots upward its coat pales, its face darkens, its fangs and claws lengthen, its ears sharpen to points, and its muzzle pushes forward. Once it finally meets its true mother, the fur turns fully white and the face darker still, mirroring her own.

Grown to adulthood, Onbu proves immensely powerful, catching swordblades barehanded the way trained shinobi do, brushing aside a band of thieves, and even holding its own against its own mother.

The trouble begins when a hawk plucks an onbaa infant from its nest, enraging the mother. Fleeing from a kunai Naruto throws during training, the bird drops the little creature onto his back, where it fastens on and takes him for its parent. No amount of prying, even with Kiba Inuzuka's help, can peel it loose. Tsunade recalls an old legend of the onbaa and shares Jiraiya's notes, which explain that the young ride their mothers' backs until they reach adulthood. Stuck with the thing, Naruto names it Onbu after the noise it makes, and it grows fixated on the red spiral of his jacket, refusing any food but fish cakes stamped with the same design.

Hoping to shake it off, Tsunade sends Naruto to clear a fortress of bandits, and during the trip Onbu swells into a towering adult, briefly letting go only to shield him from an attacker. Near Konoha the mother finally catches up and knocks Naruto off a cliff, tearing the pair apart. Reunited with her, Onbu turns savage and rounds on Naruto, until the sight of the familiar swirl snaps it back to its senses; it defends him, carries him home, and departs with its mother. Soon after, hawks begin dropping onbaa onto nearly everyone in the village, and the once-legendary animals multiply out of control.