11-year-old Kenichi Mitsuba is an average kid who goes to secondary school and struggles with his studies, he is very stubborn and is very lazy and therefore always ends up frustrating his parents and teacher. He loves to find an easy way of things. He befriends Hattori Kanzo, a ninja from the Iga Clan, and he becomes part of the Mitsuba family along with his brother, Shinzo and his ninja dog, Shishimaru. Hattori helps Kenichi with his problems, and constantly keeps an eye on him, as a good friend. The main antagonist Kemumaki, a Koga ninja and his ninja cat, Kagechiyo always troubles Kenichi, mainly because of their feud over one girl, Yumeko. Kenichi asks Hattori to take revenge as a recurring storyline in many episodes. Although Hattori is a good friend, Kenichi sometimes fights with Hattori due to misunderstandings created by Kemumaki. Sometimes Jippou, Togejirou and Tsubame help him.
Koike-Sensei visits Kenichi's house. Shishimaru loses his grip and falls on Koike-Sensei and gets him unconscious.
Shinzou loses his way and the list. So, Shishimaru and Hattori guide him. Shinzou tells everyone about his deed.
Yamamoto visits Kentaru as a schoolmate. In the night, Yamamoto robs and tries to leave but gets caught. A cop declares a reward to the family.