Kōzō Ryūzōji, headmaster of Sakaimachi Academy, is the narrative's central antagonist. His surname blends "dragon," "warehouse," and "temple," while his given name incorporates "happiness" or "good luck" and "three." Initially appearing as historian Kōdai Arima's associate, the original Ryūzōji was killed and replaced by an interdimensional being who assumed his identity and memories. This imposter manipulates events from his position of authority.

He wields a potent hypnotic ability, "Narb" ("Brain" spelled backwards), functioning like covert mind control to influence others. His primary goal is securing the Reflector Device, an otherworldly artifact capable of cross-dimensional travel sent to Takuya Arima by his missing father, making it the focus of his schemes.

Pulling strings from the shadows, Ryūzōji pressures Ayumi Arima concerning her work at Geo Technics, a company investigating Mount Sankaku and its psychite deposits. His manipulations push Ayumi into situations of extreme stress, potentially triggering tragic outcomes in certain timelines. His influence also extends to Mitsuki Ichijō, whose enigmatic connection to him invariably results in her death across all timelines, despite attempts to intervene.

His true motivations surface during the collision of worlds when Dela Grante's orbit intersects Earth. As an immortal being, he disrupts the ritual intended to prevent catastrophe—a ritual requiring Yu-no's sacrifice to the world's AI system. He aims to exploit this event for personal gain, but his interference ultimately fails when interdimensional law enforcement agent Eriko Takeda kills him during the confrontation.

His background as an interdimensional entity remains largely unexplained, with no definitive origin provided. Throughout the narrative, he maintains a consistent role as an antagonist driven by self-preservation and the pursuit of power, without significant personal development or redemption.