SpoilerRyuuta is given a small arc in conjunction with Maria Alucard and Morihito Inugami's back-stories in season two. Ryuuta keeps a mangled foot in stasis within the morgue, along with a blood-stained white trenchcoat. We discover that when he was little, his older brother was partners with Mikuriya in dealing with criminal supernatural cases. His brother is bitten by a vampire-like demon, and becomes a demon himself, infecting others in the hospital treating him. The new oni horde perishes, however, when the sun rises. Ryuuta keeps his brother's final body part for study, and his coat for remembrance.
This tragedy leads Ryuuta to become a forensic student in order to join the police force with Mikuriya, so that the both can hunt the monster that killed his brother. They eventually track down Maria Alucard, but she is saved by Inugami, who warns enraged Ryuuta and sensible Mikuriya that she is not the demon they seek.