"Hiiragi-senpai to Ofutari-sama" centers on the relationship dynamics between Hiiragi, a reserved and diligent high school student, and Ofutari, a cheerful and outgoing classmate who harbors a secret. The narrative explores their evolving bond as Ofutari reveals that she is actually two people sharing one body—a pair of twins who alternate control of their shared physical form. This revelation complicates their interactions, as Hiiragi must navigate the distinct personalities and preferences of each twin while maintaining a semblance of normalcy in their daily lives.

The story delves into the challenges of communication and trust, as Hiiragi learns to distinguish between the twins and adapt to their individual quirks. One twin is more assertive and confident, while the other is shy and introspective, creating a dynamic that shifts depending on who is in control. As Hiiragi grows closer to both, the twins' unique situation raises questions about identity, individuality, and the nature of relationships. The series balances lighthearted moments with deeper emotional undertones, examining how the characters cope with their circumstances and support one another.

Themes of acceptance and understanding are central to the narrative, as Hiiragi and the twins navigate the complexities of their unconventional relationship. The story progresses through a series of everyday scenarios, from school events to personal challenges, highlighting the characters' growth and the deepening of their connection. The twins' shared existence serves as a metaphor for the duality of human nature, while Hiiragi's role as a mediator and confidant underscores the importance of empathy and patience in fostering meaningful relationships. The series maintains a grounded tone, focusing on character development and interpersonal dynamics rather than relying on fantastical elements to drive the plot.