"Basilisk: Ōka Ninpōchō" is a historical fantasy anime set in 17th-century Japan during the early Edo period. The story revolves around a bitter feud between two rival ninja clans, the Iga Tsubagakure and the Kouga Manjidani, who have been locked in a centuries-long conflict. The clans are forced into a deadly confrontation when the Tokugawa shogunate, seeking to determine the successor to the throne, orders each clan to select ten of their strongest warriors to compete in a brutal battle. The last surviving clan will earn the right to influence the next shogun.

The Iga clan is led by Oboro, a gentle and compassionate kunoichi who possesses the mystical "Eyes of Destruction," a power that can petrify her enemies. Despite her abilities, Oboro is reluctant to embrace violence and seeks peace between the clans. Her betrothed, Gennosuke of the Kouga clan, is a skilled warrior with the "Eyes of Insight," which allow him to predict and counter his opponents' movements. Gennosuke shares Oboro's desire for reconciliation, but the escalating conflict forces both to confront their loyalties and ideals.

As the battle unfolds, the ten warriors from each clan employ their unique ninja techniques and supernatural abilities to eliminate their rivals. The Iga clan includes fighters such as Hotarubi, a master of fire-based techniques, and Tenzen, a ruthless and ambitious leader. The Kouga clan features warriors like Hyoma, a swordsman with a tragic past, and Okoi, a seductive and deadly kunoichi. The clashes between these warriors are intense and often fatal, with each death further deepening the animosity between the clans.

Amid the carnage, Oboro and Gennosuke struggle to maintain their love and hope for peace, even as they are drawn into the violence. Their relationship becomes a central theme, highlighting the personal toll of the feud. The story explores themes of loyalty, sacrifice, and the devastating consequences of hatred and vengeance. The narrative builds toward a tragic and inevitable conclusion, as the clans' mutual destruction becomes a reflection of the futility of their conflict.

"Basilisk: Ōka Ninpōchō" combines historical elements with supernatural action, creating a tale of love and war that is both emotionally charged and visually striking. The series delves into the complexities of its characters, portraying them as multifaceted individuals caught in a cycle of violence they cannot escape. The result is a compelling and tragic story that resonates with themes of human conflict and the cost of enduring enmity.