"Oyajina! Otaku no Shiro-chan no Baai" centers on the life of Shiro, a young otaku who is deeply immersed in anime, manga, and gaming culture. Shiro’s life takes an unexpected turn when he is suddenly tasked with raising his younger half-sister, Hina, after their parents pass away. Despite his initial reluctance and lack of experience in caregiving, Shiro must navigate the challenges of balancing his otaku lifestyle with the responsibilities of being a guardian.

The narrative explores the dynamics between Shiro and Hina as they adjust to their new living situation. Shiro’s otaku habits often clash with the practical needs of raising a child, leading to humorous and heartfelt moments. Hina, on the other hand, is portrayed as a bright and curious child who gradually becomes influenced by Shiro’s interests, developing her own appreciation for otaku culture. Their relationship evolves as they learn to understand and support each other, with Shiro growing into a more responsible figure while still maintaining his passion for his hobbies.

The story also introduces a supporting cast of characters, including Shiro’s friends and fellow otaku, who provide comedic relief and occasional assistance in his parenting journey. These characters often highlight the contrast between Shiro’s carefree otaku lifestyle and the demands of his new role. The manga delves into themes of family, responsibility, and the blending of personal passions with real-world obligations, presenting a balanced portrayal of otaku culture without romanticizing or criticizing it.

Throughout the series, Shiro’s growth as a guardian is depicted through his efforts to create a stable and nurturing environment for Hina, while also finding ways to share his interests with her. The narrative maintains a lighthearted tone, blending humor with moments of genuine emotional depth, as it chronicles the everyday challenges and triumphs of their unconventional family life.