Ryoma, known as the "Dokugan Ryū" (One-Eyed Dragon), serves as a core member of the Fūma ninja clan. His missing eye marks him, sharing this trait with the legendary Date Masamune, though their names differ in kanji. Within the clan, Ryoma stands as the most focused, disciplined, and respectful member, adhering strictly to traditional "Shinobi Law." This rigid dedication to duty and combat often renders him emotionally reserved or machine-like.

His primary role sees him engaged in the Fūma clan's ancient feud against the rival Yasha clan. He directly confronts the Yasha and acts as a key fighter in the battles stemming from the conflict between Hakuo Academy and Seishikan High School. Ryoma wields the strongest psychic abilities among the Fūma ninja, with his signature technique being the powerful psychic attack "Fūma Shikyoken" (Four Demons Fist).

A significant development occurs through his interactions with Ranko Yagyū, a Hakuo Academy student. Her attempts to show him kindness and compassion challenge his strict adherence to the impersonal codes of Shinobi Law. This relationship gradually compels Ryoma to confront and acknowledge his own humanity beyond being a mere clan weapon.

Ryoma survives the initial clan war against the Yasha (depicted in the Yasha Chapter). He later participates as one of the Cosmo Warriors in the larger-scale Sacred Sword War, battling the Chaos Warriors for control of the ten sacred swords. He ultimately endures the brutal Fūma Rebellion Chapter, a coup staged by the New Fūma Clan. By this final arc's conclusion, Ryoma is one of only two major Fūma clan members confirmed to have survived the rebellion's widespread fatalities, alongside Kojirō.