Kenichi Mitsuba, a stubborn and lazy 10-year-old Tokyo elementary student, constantly hunts for shortcuts to evade effort, clashing with parents and teachers due to his struggles in schoolwork and sports. His passions lie in photography and an earnest, unrequited crush on classmate Yumeko Kawai—a devotion that sparks frequent clashes with his rival, Koga ninja Kemumaki.

When Iga ninja Kanzo Hattori moves into his home, Kenichi forges a tight bond with him, leveraging Hattori’s loyalty to settle grudges against Kemumaki or untangle self-made misunderstandings. His mischievous dynamic with Hattori’s brother Shinzo and ninja dog Shishimaru blends playful antics with teamwork, often mending the chaos they create.

Kenichi’s reckless theft of a mystical ninja star ignites destructive confrontations with foes like Vasu, leveling Yumeko’s home and triggering explosive battles. His rivalry with Kemumaki intensifies through cunning schemes and contests, frequently quelled by Hattori’s mediation. Despite his flaws, Kenichi reluctantly teams with allies such as Jippou and Tsubame to thwart greater threats.

Sporting glasses and a cap that mirror his carefree attitude, Kenichi navigates life through a mix of resourcefulness and reliance on Hattori, while balancing rivalry with Kemumaki and persistent affection for Yumeko. Though his growth remains static, his role hinges on tackling everyday trials with ninja-backed ingenuity.