In year 9 of the Hanpeï era, Karamaru-kun, a four-year-old ninja, has to bring mushrooms in town and sell them to buy medicins and cigarettes for his sick grandfather. On the way, he meets a car stealer who thinks he is ninja as well. The car stealer helps Karamaru to stop a gang of three ninja thieves who took his mushrooms (they do not steal the car because none of them has a driving license). In the end, convinced that he must be a good example to the young boy, the car stealer brings the car to the police and offers Karamaru to become his disciple.

(Source: Dragon Ball Wiki)