"Aka-chan to Boku" centers on Takuya Enoki, an 11-year-old boy who lives with his father and younger brother, Minoru, after their mother passes away. Takuya is mature for his age, often taking on responsibilities beyond his years, including caring for Minoru. Their lives take a significant turn when their father hires a live-in babysitter, 17-year-old Marina Kawamoto, to help manage the household. Marina, a high school student, initially struggles with the demands of the job but gradually forms a close bond with the boys.

The series explores the dynamics of this unconventional family as they navigate daily life, school, and personal challenges. Takuya, despite his young age, often acts as a stabilizing force, balancing his role as a brother with his own childhood experiences. Minoru, on the other hand, is more carefree and mischievous, providing a contrast to Takuya's seriousness. Marina's presence introduces a maternal figure into their lives, and her growth as a caregiver becomes a central theme.

Throughout the series, the characters face various situations that test their relationships and resilience. Takuya deals with the pressures of school and the emotional weight of losing his mother, while Marina grapples with her own insecurities and the responsibilities of her role. Minoru's antics often bring lighthearted moments, but he also learns valuable lessons about family and responsibility. The narrative emphasizes themes of family, growth, and the importance of support systems, portraying the characters' development in a realistic and heartfelt manner.

The interactions between Takuya, Minoru, and Marina form the core of the story, highlighting the challenges and joys of their evolving relationships. The series balances humor and emotional depth, offering a nuanced portrayal of family life and the impact of caregiving on both the caregiver and the children. Through its exploration of these themes, "Aka-chan to Boku" presents a touching and relatable depiction of an unconventional family finding their way together.