"Ninjaman Ippei" is a comedic anime series centered around Ippei, a young ninja-in-training from the Iga clan, who is sent to the modern world to protect a girl named Yuka. The series blends traditional ninja themes with contemporary settings, creating a humorous contrast between Ippei's outdated ninja skills and the challenges of modern life. Ippei's mission is to guard Yuka from the Koga clan, a rival ninja group seeking to eliminate her due to a prophecy that foretells her future role in defeating them.

The narrative unfolds as Ippei adapts to the modern world, often misunderstanding technology and social norms, which leads to comedic situations. Despite his clumsiness and lack of conventional ninja prowess, Ippei's determination and unconventional methods often save the day. Yuka, initially unaware of her significance, gradually becomes more involved in the conflict as the Koga clan's attacks intensify. The series features recurring antagonists from the Koga clan, each with unique abilities and comedic quirks, who frequently clash with Ippei in over-the-top battles.

Throughout the series, Ippei's growth as a ninja is juxtaposed with his growing bond with Yuka and his attempts to reconcile his traditional upbringing with the demands of modern life. The episodic structure balances humor, action, and occasional moments of heartfelt connection, making it accessible to a wide audience. The dynamic between Ippei's earnestness and Yuka's grounded personality drives much of the series' charm, while the rivalry with the Koga clan provides a consistent source of conflict and comedic tension.