Ninja Hattori-kun follows the life of Kanzo Hattori, a young Iga ninja who leaves his home in the mountains to live in Tokyo. He becomes a live-in companion to Kenichi Mitsuba, a kind-hearted but lazy and academically struggling elementary school boy. Hattori uses his ninja skills, gadgets, and wisdom to help Kenichi navigate the challenges of school life, bullies, and his unrequited crush on Yumeko-chan. The series centers on the comedic rivalry between Hattori and his nemesis, Kemumaki, a Koga ninja who also lives in the city and frequently uses his own ninja techniques to cause trouble for Kenichi. Alongside Hattori's younger brother, Shinzo, and their ninja dog, Shishimaru, the group engages in daily adventures that blend slapstick humor with heartwarming lessons about friendship, perseverance, and the importance of hard work.