The episode begins with a bird flying by and snatching something out of a nest. After the bird flies off a creature is shown and growls at the bird as it flies off. Naruto is then shown training in the forest. The bird that was shown earlier flies by and startles Naruto, so he throws a kunai at it before he realizes it is a bird. After the kunai flies past the bird, startling it, it drops what it was carrying. The thing the bird was carrying lands on Naruto, who thinks the bird crapped on him. He dismisses the thought and heads back to the village. When he gets there people start looking at him funny.
Naruto walks around a corner to have Akamaru barking at him. Naruto asks Kiba what is wrong with Akamaru and Kiba tells him that Akamaru says Naruto stinks. Sakura comes and talks about Naruto having a lot of free time since he has not received any missions lately. She tells Naruto that part of his clothing is torn and she will fix it for him if he wants. Naruto goes nuts since this is the first nice thing Sakura has done for him, according to him. As Naruto gets close up to Sakura to tell her he would like that a little furry hand reaches out and grabs Sakura. Sakura gets angry thinking Naruto did it and kicks him. Naruto says it was not him and Sakura asks what the furry hands armpits were. Naruto then goes nuts because there is some creature on his back. Kiba tries to get it off but cannot so they go and see Tsunade.
Tsunade tells them about the legend of the Onbaa and tells them that Jiraiya had gone to look for one a long time ago. A flashback then occurs and Jiraiya and Tsunade are arguing about the existence of the Onbaa. Orochimaru then speaks up and says that Jiraiya will find the Onbaa. Jiraiya leaves and the flashback ends. Tsunade then shows the gang some notes that Jiraiya took on the Onbaa. She also tells the group that the notes were fakes and Jiraiya had never met an Onbaa. Naruto finds out that the Onbaa will not leave his back until it grows to an adult The problem with this is that its average adult is 3 meters tall.
After Naruto leaves he runs into Hinata who says she heard a funny rumor about him. Naruto gets a little angry about this and asks about the rumor. Hinata says that people have been saying he has a kid. Naruto shows Hinata the Onbaa and she faints. Naruto runs over to get her to come around. When Hinata finally wakes up she sees the Onbaa again and faints again.
That night as Naruto is about to eat some pizza the Onbaa takes it as a very good time to pee. Naruto then takes a bath with his clothes on and thinks about if he has to take a bath every time the Onbaa has to use the bathroom. He then goes out to eat and is told by the manager of where he eats at that "no pets are allowed". The waitress says the critter is cute and asks what its name is. Naruto says that since it says "Onbu" a lot he will name it that.
The next day Tsunade observes Naruto cleaning the great stone faces and notices that the Onbaa has grown a lot. She then decides to send Naruto on a mission to Yamabuki to get rid of some bandits. Naruto takes it as some attempt to get rid of the Onbaa. Tsunade denies this and sends him on his mission.
Naruto leaves with everyone watching him leave. The next segments show Naruto and Onbu as they travel to Yamabuki. Onbu has grown a lot when it and Naruto reach the place where Naruto has to get rid of the bandits. Naruto calls out the bandits and tells them who he is and the bandits attack him. Naruto uses his Kage Bunshin no Jutsu and then the bandits destroy the Onbu on the clones' backs. Naruto gets mad and beats up all the bandits. One attacks from behind and Onbu saves Naruto.
Naruto leaves and is attacked from behind by Onbu's mom. A fight starts and Naruto spends most of it running. Onbu's mom knocks Naruto over the edge of a cliff and then changes Onbu into a savage monster like her. Naruto climbs up the cliff to find Onbu acting like its mother. Naruto then tries to change Onbu back. Onbu's mother attacks Naruto only to be stopped by Onbu. Naruto faints and wakes up to being carried by Onbu. He then falls back asleep. He wakes up outside the gate of the village and to Onbu and its mother walking away. When Naruto goes and sees Tsunade he finds that everyone has Onbaa on their backs. Tsunade then yells Naruto to tell her how he got his Onbaa off his back. All the Onbaa are shown on the villagers back and then the episode ends.