"Ninpu Kamui Gaiden" is a dark and action-packed anime series set in feudal Japan, blending historical elements with supernatural themes. The story centers on Kamui, a skilled ninja who belongs to the Fuma clan, a group of outcasts and assassins. Kamui is betrayed by his clan after being falsely accused of a crime he did not commit, leading to his exile and a vow of vengeance. As he navigates a world filled with political intrigue, rival ninja clans, and supernatural forces, Kamui becomes a wandering warrior, seeking both redemption and retribution.

The narrative explores Kamui's internal struggle as he grapples with his identity and the moral ambiguity of his actions. Along his journey, he encounters various allies and enemies, including other ninja clans, samurai, and mystical beings. The series delves into themes of loyalty, betrayal, and the cost of vengeance, as Kamui's quest for justice often puts him at odds with his own humanity. The plot is driven by intense battles, intricate schemes, and the ever-present threat of the supernatural, which adds a layer of mysticism to the historical setting.

Key characters include Kamui, the protagonist whose tragic past fuels his relentless pursuit of justice; Genjuro, a rival ninja with a complex relationship to Kamui; and Sayaka, a mysterious woman whose connection to Kamui adds emotional depth to the story. The series also features a range of antagonists, each representing different facets of the corrupt and chaotic world Kamui seeks to dismantle. Through its exploration of Kamui's journey, "Ninpu Kamui Gaiden" presents a gritty and compelling tale of survival, honor, and the consequences of one's choices in a world where the line between good and evil is often blurred.