"I Don't Like You At All, Big Brother!!" is a manga series that explores themes of family, love, and personal growth through a complex sibling relationship. The story centers on Hikari, a high school girl who harbors deep resentment toward her older stepbrother, Sakuya. Their relationship is strained due to Sakuya's cold and dismissive attitude, which contrasts sharply with his popularity and charm at school. Hikari struggles to reconcile her feelings of anger and frustration with the growing realization that her emotions toward Sakuya may be more complicated than she initially thought.

As the narrative progresses, the dynamic between Hikari and Sakuya evolves, revealing layers of unresolved tension and unspoken emotions. Sakuya's aloof demeanor gradually softens, and glimpses of his vulnerability and care for Hikari begin to surface. The story delves into their shared past, uncovering the reasons behind Sakuya's distant behavior and the impact of their family's blended structure on their relationship. Themes of jealousy, misunderstanding, and the struggle for emotional connection are explored as the siblings navigate their evolving bond.

Supporting characters, including friends and classmates, play significant roles in shaping the story. These characters often serve as catalysts for Hikari and Sakuya's personal growth, providing external perspectives that challenge their preconceived notions about each other. The manga balances moments of humor and lightheartedness with deeper emotional exploration, creating a narrative that is both engaging and introspective.

The plot unfolds through a series of interconnected events, ranging from everyday school life to more dramatic confrontations, which gradually bring Hikari and Sakuya closer. The resolution of their conflicts is not immediate, and the story emphasizes the importance of communication and understanding in overcoming emotional barriers. By the end of the series, the relationship between Hikari and Sakuya undergoes significant transformation, reflecting their individual growth and the deepening of their familial bond.