During the Hanpeï era's ninth year, Karamaru-kun, a young ninja at the tender age of four, embarks on a mission to sell mushrooms in town. His goal? To procure medicine and cigarettes for his ailing grandfather. Along the way, he crosses paths with a car thief who mistakes him for a fellow ninja. Together, they thwart a trio of ninja bandits who have pilfered Karamaru's mushrooms (fortunately, the thieves refrain from stealing the car due to their lack of driving licenses). Ultimately, recognizing the need to set a positive example for the boy, the car thief surrenders the stolen vehicle to the authorities and proposes to take Karamaru under his wing as his apprentice.