"Fūma no Kojirō" is a manga series set in feudal Japan, blending historical elements with supernatural themes. The narrative centers on Kojirō, the young leader of the Fūma clan, a group of ninja warriors known for their stealth and combat prowess. The Fūma clan is locked in a bitter rivalry with the Yasha clan, a powerful and malevolent group seeking to dominate Japan through dark rituals and supernatural means. The conflict between these two clans forms the core of the story.

Kojirō is portrayed as a determined and skilled warrior, driven by a sense of duty to protect his clan and uphold their honor. His journey begins when the Yasha clan launches a brutal attack on the Fūma, decimating their ranks and leaving Kojirō as one of the few survivors. Vowing revenge, Kojirō embarks on a mission to rebuild the Fūma clan and confront the Yasha. Along the way, he gathers allies, including other surviving Fūma members and warriors from rival clans who share his goal of stopping the Yasha's tyranny.

The Yasha clan, led by the ruthless and enigmatic Ryūma, employs dark magic and demonic powers to achieve their goals. Their ultimate aim is to resurrect an ancient demon god, which would grant them unstoppable power. Kojirō's quest to thwart this plan takes him across Japan, where he faces numerous challenges, including battles with Yasha assassins, treacherous terrain, and internal conflicts within his own clan. The series emphasizes themes of loyalty, sacrifice, and the struggle between good and evil, as Kojirō and his allies fight to prevent the Yasha from plunging the world into chaos.

The manga features a mix of intense martial arts combat, supernatural elements, and strategic warfare. Kojirō's growth as a leader and warrior is a central focus, as he learns to balance his desire for revenge with the responsibility of protecting his people. The Yasha clan's use of dark magic and demonic forces adds a layer of supernatural tension, creating a stark contrast to the Fūma's reliance on traditional ninja techniques and human ingenuity.

Key characters include Kojirō's loyal companions, such as the skilled swordsman Ryūzō and the resourceful ninja Kagero, who provide support and camaraderie throughout the journey. The Yasha clan's leaders, particularly Ryūma and his lieutenants, serve as formidable antagonists, each possessing unique abilities and motivations that drive the conflict forward. The interplay between these characters, along with the high-stakes battles and moral dilemmas, creates a compelling narrative that explores the complexities of honor, power, and survival in a war-torn era.