Kōta Takamura is a high school student and the male lead of the series. He becomes the stepbrother of Aika Takamura after his father, Yoshiyuki, remarries Aika’s mother, Misaki. From the start, Kōta is portrayed as a disciplined, highly logical, and argumentative young man. His personality is described as “straight-laced” and “certinho” (proper), which stands in stark contrast to Aika’s flashy, foul-mouthed gyaru demeanor. This opposition defines much of the early tension between them: Kōta is frequently exasperated by Aika’s unpredictable and bratty behavior, especially when their parents are away. Despite his cold or dismissive exterior, Kōta possesses a genuine caring nature that gradually emerges as he learns to navigate his new family dynamic.

His motivation initially centers on simply enduring the chaotic household, but an unspecified incident triggers a shift in his relationship with Aika. As Aika begins to warm up to him, Kōta’s protective older-brother instincts surface, and he starts to feel a sense of responsibility toward her. This development forms the emotional core of the story, as the two stepsiblings move from constant conflict to a closer, more complicated bond. Kōta’s role is that of the grounded, rational counterweight to Aika’s impulsiveness, and his growth involves learning to express his kindness more openly. While he does not possess any supernatural or combat abilities, his notable traits include his logical reasoning, moral steadfastness, and a subtle emotional maturity that allows him to eventually accept and care for his stepsister. His relationship with his father Yoshiyuki and stepmother Misaki is supportive but secondary to the central dynamic with Aika. Throughout the series, Kōta’s development is marked by his gradual willingness to step beyond his rigid boundaries, ultimately embracing his role as a brother even as the relationship takes on romantic and intimate overtones.