"Ōya-san to Boku" centers on the daily lives of a young boy named Rintarou and his interactions with his landlady, Ōya-san, who oversees the apartment complex where he resides. Rintarou, a quiet and reserved child, lives alone in his apartment after his parents moved abroad for work, leaving him to manage his daily life independently. Despite his solitude, he finds companionship and guidance in Ōya-san, who takes on a maternal role, ensuring his well-being and offering support in various aspects of his life.

The series unfolds through a series of episodic vignettes, each highlighting the mundane yet heartwarming moments shared between Rintarou and Ōya-san. Their relationship is characterized by a blend of humor, warmth, and occasional misunderstandings, as Ōya-san often goes to great lengths to care for Rintarou, sometimes overstepping boundaries in her eagerness to help. These interactions are punctuated by the presence of other tenants in the apartment complex, who add depth to the narrative through their own quirks and relationships with the main characters.

Rintarou’s experiences range from navigating school life to dealing with everyday challenges, all while Ōya-san provides a steady, albeit unconventional, source of support. Her overbearing yet well-intentioned nature often leads to comedic situations, but it also underscores the genuine care she has for Rintarou. The series balances lighthearted moments with subtle emotional undertones, exploring themes of family, responsibility, and the importance of human connection.

The dynamic between Rintarou and Ōya-san forms the core of the narrative, with their evolving relationship serving as the primary focus. While the story lacks a central overarching plot, its strength lies in its slice-of-life portrayal of their bond, offering a relatable and endearing depiction of everyday life. The series captures the essence of found family, emphasizing how meaningful relationships can emerge in unexpected places.