Ryoma Kogure is a ninja of the Hagakure clan, wielding the Spear of Sorcery, one of three mystical weapons destined to combat demonic forces threatening feudal Japan. As the son of Genyusai, leader of Hagakure village, he witnesses his father's death during an Oboro ninja invasion led by Jinnai Saegusa. The attack devastates his community, leaving Ryoma one of the few survivors forced to flee.

His younger sister, Kikyo, also perishes in the conflict, dying in his arms after sacrificing herself to protect Ayame from Jinnai. This profound loss fuels Ryoma's determination. He later develops unrequited feelings for Kayo Momochi, a Koga ninja and sister of Iga leader Tanba Momochi. When Kayo's body is possessed by the Oboro member Masago, Ryoma is compelled to kill her at her own request, ending her suffering and preventing further slaughter of allies.

Headstrong yet driven by a strong sense of justice and loyalty, Ryoma forges a bond with fellow survivors Ayame and Sakon. Together, they unite their enchanted weapons against the demon warlord Oda Nobunaga and the Oboro. Ryoma's combat prowess faces constant tests, including a severe injury sustained while defeating the Oboro ninja Kagami.

In the final confrontation against the true antagonist, Ranmaru Mori, Ryoma sacrifices his life. His dying thoughts focus on his sister Kikyo, highlighting the personal losses that defined his path. This act helps seal the gate to the underworld, thwarting Ranmaru's centuries-long plan.

The manga adaptation retains these core elements, though narrative details may differ from animated versions. Across all media, Ryoma's story emphasizes duty, sacrifice, and the weight of vengeance.