Set in Sengoku period Japan, the film revolves around an 8-year-old boy named Rantaro (Kato Seishiro) who's born into a small-time ninja family. Following through on his parents' expectation that he will also become a ninja, he's enrolled at a special school to learn the art of ninjutsu. However, he often gets distracted from his studies by two equally clumsy friends, Shinbee (Kimura Fuuta) and Kirimaru (Hayashi Roi). When a 4th year student namedSaito Takamaru (Mizoguchi Takuya)—the son of a barber and member of a clan of assassins—appears, it becomes necessary for Rantaro to rise up to save a friend.