"My Friend's Little Sister Has It In for Me!" centers on the life of Akiteru Kusanagi, a high school student and aspiring light novel author. Akiteru collaborates with his childhood friend, Mashiro Shiromaru, who illustrates his stories. The two form a creative duo, aiming to achieve success in the competitive world of light novels. Their partnership is professional yet tinged with unresolved feelings from their shared past.

The story takes a turn when Akiteru moves into a dormitory for aspiring creators, where he encounters Mashiro’s younger sister, Iroha Shiromaru. Iroha, a popular and outgoing girl, harbors a mischievous streak and a penchant for teasing Akiteru. Despite her playful demeanor, Iroha’s actions often complicate Akiteru’s life, creating a dynamic filled with misunderstandings and comedic tension. Her presence disrupts the equilibrium between Akiteru and Mashiro, adding layers of complexity to their relationship.

As the narrative progresses, Akiteru navigates the challenges of balancing his creative ambitions with the interpersonal dynamics surrounding him. Mashiro, who is reserved and deeply focused on her work, contrasts sharply with Iroha’s lively and unpredictable nature. The interactions between the three characters drive much of the story’s humor and emotional moments, exploring themes of friendship, rivalry, and unspoken feelings.

The series also introduces other characters who contribute to the dormitory’s vibrant atmosphere, including fellow creators and friends who influence Akiteru’s journey. These interactions provide additional depth to the story, highlighting the struggles and triumphs of pursuing creative careers in a competitive environment.

Throughout the series, the focus remains on the evolving relationships between Akiteru, Mashiro, and Iroha, as well as their individual growth. The blend of comedy, romance, and slice-of-life elements creates a narrative that balances lighthearted moments with more introspective themes, offering a multifaceted portrayal of young creators navigating their dreams and relationships.