"Ninku" is a manga series set in a fictional world where ninja clans wield unique powers known as Ninku techniques. The story begins with the aftermath of a great war between the Ninku clans and the imperial army. The Ninku clans, once feared and respected, were nearly eradicated after being betrayed by their leader, Emperor Hōō. The protagonist, Fusō, is a young Ninku master who survived the war and now seeks to rebuild his clan while confronting remnants of the imperial forces and other adversaries.

Fusō is accompanied by a group of allies, each with their own Ninku abilities. Among them are Rihoko, a skilled fighter with a tragic past, and Aicho, a former imperial soldier who defects to Fusō's side. Together, they face various challenges, including battles against powerful enemies who seek to exploit or destroy the remaining Ninku clans. The narrative explores themes of loyalty, betrayal, and the struggle to preserve a fading way of life.

The plot unfolds through a series of arcs, each focusing on different conflicts and character developments. Fusō's journey takes him across diverse landscapes, from war-torn villages to hidden strongholds, as he uncovers secrets about the Ninku clans and the true motives behind their downfall. The series balances action-packed fight sequences with moments of introspection, delving into the personal histories and motivations of its characters.

As the story progresses, Fusō and his allies confront increasingly formidable foes, including rogue Ninku users and remnants of the imperial army. The climax of the series revolves around a final confrontation with Emperor Hōō, whose betrayal set the events of the story in motion. The resolution ties together the various narrative threads, offering closure to the characters' arcs while leaving room for the legacy of the Ninku clans to endure.

The manga's world-building is detailed, with a rich history of the Ninku clans and their techniques. The characters are distinct, with their own unique abilities and personal struggles, contributing to the series' dynamic and engaging narrative. "Ninku" combines elements of action, adventure, and drama, creating a compelling story that appeals to fans of the genre.