Hattori-kun received a letter from Iga's father asking him to take his friends and return home for spring break. Hattori-kun leaves for Iga with his younger brothers Shinzo, Kenichi, Yumeko-chan, and others. However, a suspicious shadow stares at the group... He is a subordinate of the scientific ninja Mechamaro, who has replaced the power of ninjutsu with the power of science. Mechamaro was plotting to confront Hattori-kun in order to prove the strength of scientific ninjas. And in order to occupy Iga no Sato, Hattori-kun sends a fake letter...
Tiré des journaux intimes d'officiers subalternes et de simples soldats jugés et emprisonnés pour crimes de guerre, le film pose la question de la véritable responsabilité de ces condamnés qui ont le plus souvent exécuté les ordres de leur hiérarchie.