"Nai-Chichi" is a manga series that explores themes of family, responsibility, and unconventional relationships. The story centers around Keisuke, a young man who unexpectedly becomes the guardian of his younger half-sister, Riko, after their parents pass away. Keisuke, initially unprepared for the responsibilities of parenthood, struggles to balance his personal life with the demands of raising a child. Riko, a bright and energetic girl, relies on Keisuke for emotional and practical support, creating a dynamic that evolves as they navigate their new lives together.

The narrative delves into the challenges Keisuke faces as he adapts to his role as a surrogate father. His efforts to provide for Riko while maintaining his own aspirations and relationships form the core of the story. The series portrays their daily lives, highlighting moments of tension, growth, and bonding. Keisuke’s interactions with Riko often reveal his vulnerabilities and strengths, as he learns to prioritize her well-being over his own desires.

Secondary characters, including Keisuke’s friends and acquaintances, play significant roles in shaping the story. These characters provide support, advice, and occasional conflict, adding depth to the narrative. The series also explores societal perceptions of single guardianship and the stigma surrounding unconventional family structures, offering a nuanced perspective on these issues.

Throughout the manga, the relationship between Keisuke and Riko is central, with their bond deepening as they overcome various obstacles. The story balances moments of humor, drama, and introspection, creating a multifaceted portrayal of their lives. Themes of sacrifice, resilience, and the complexities of familial love are consistently woven into the narrative, making "Nai-Chichi" a compelling exploration of parenthood and personal growth.