10-year old Ken'ichi Mitsuba is an average kid who goes to elementary school and struggles with his studies. Meanwhile a little ninja named Kanzo Hattori, Shishi-maru (a ninja dog) and Kanzo's little brother Shinzo befriend Ken'ichi. Hattori is now a part of the Mitsuba family along with his brother Shinzo, and his ninja dog, Shishi-Maru. Hattori helps Ken'ichi with his problems, and constantly keeps an eye on him, as a good friend. Yumeko-chan is the girlfriend of Ken'ichi. Kemumaki, a Koga Ninja and his ninja cat Kagekiyo always trouble Ken'ichi. Ken'ichi asks Hattori to take revenge.