Ryuya is the primary guardian for Kannabi-no-Mikoto (Kanna), a winged being sheltered at a shrine. Abandoned to die as a child, he was rescued by a traveling monk. Ryuya witnessed bandits murder this monk during a robbery. Surviving alone, he stole a sword and became a mercenary, developing exceptional combat skills that allowed him to subdue opponents non-lethally even when outnumbered. His proficiency led to recruitment by the imperial army as a bodyguard for high-ranking officials, culminating in his assignment to protect Kanna.

While serving at Kanna's shrine, Ryuya grew suspicious upon being ordered to compile documents about her relocation. Anticipating betrayal, he orchestrated an escape with Kanna and her caretaker Uraha just before mercenaries attacked and destroyed the shrine. This coup attempt targeted winged beings like Kanna as symbols of the emperor's authority. After escaping, Kanna extracted a vow from Ryuya never to kill while protecting her, a pledge he rigorously upheld despite life-threatening confrontations during their flight.

Unspoken romantic tension existed between Ryuya and Kanna, though her expressions of interest were frequently interrupted. With Uraha, they located Kanna's mother at a Buddhist shrine. Ryuya incapacitated the guarding monks non-lethally but sustained a back wound from one he spared. This injury later worsened due to a curse transmitted during contact with Kanna's mother, who was mortally wounded in a subsequent ambush. After Kanna sacrificed herself by flying skyward to divert imperial forces—resulting in her banishment to a dream realm—Ryuya and Uraha dedicated themselves to finding a way to break her curse.

Their search led them to a temple where they learned the curse could not be lifted for centuries. Uraha proposed a multi-generational solution, prompting Ryuya to conceive a child with her to continue their mission. As Ryuya's curse-induced illness progressed, he reflected on finding unexpected happiness in his life with Uraha and their purpose. He died before the child's birth, his final moments envisioning a reunion with Kanna in the sky.

Across adaptations, Ryuya's narrative varies. In the visual novel and main anime, his partnership with Uraha evolves into a familial bond, with their descendant Yukito Kunisaki inheriting the quest to save Kanna's reincarnation. Conversely, the film adaptation depicts Ryuya exclusively as Kanna's lover, omitting romantic ties to Uraha and altering his death to a spear wound during her escape. The film also attributes Yukito's puppet-controlling abilities to Ryuya instead of Uraha. The "Air in Summer" special elaborates on the journey period, emphasizing Ryuya's protective dynamic with Kanna and Uraha through comedic and mundane incidents, without introducing new character developments beyond the core storyline.