Ryōta is Misuzu's younger brother, possessing an androgynous appearance that frequently results in visual gender ambiguity. He lives with his family—his mother and sister—where the self-proclaimed alien Naoko-san has replaced his elder sister Naoko. Naoko-san frequently subjects Ryōta to unconventional and demanding commands. These orders involve inappropriate or absurd tasks, like attempting to suck nasal fluids from a hay-fever-stricken Misuzu using a straw under Naoko-san's direction.

His role includes being coerced into buying adult material while disguised in mechanical armor, leading to public incidents. One such incident involved a bomb detonation at an adult video shop after he pressed an incorrect button during age verification, reported as terrorism-related news, though Naoko-san dismissed it as a pornography-buying inconvenience. Ryōta exhibits naive compliance with Naoko-san's orders, reflecting his gullibility and lack of critical assessment toward her authority. He displays specific anxieties about his genitalia, pondering potential inadequacies despite his youth, often triggered by Naoko-san's comments provoking his self-consciousness.

During family outings or Naoko-san's orchestrated missions, Ryōta is often burdened with physically demanding tasks, such as carrying heavy sacks later revealed to contain trivial items like alien confectionery. His presence is sometimes overlooked within family dynamics, as when Misuzu realized they had forgotten him during chaotic events. Emotionally, Ryōta expresses disappointment when plans like visiting Destinyland are canceled due to their father's work. Naoko-san exploits this disappointment by offering interdimensional travel to the theme park using alien technology, though her interventions typically lead to further mishaps, such as extended unconsciousness from experimental devices.