"R-15" is a manga series that revolves around Taketo Akutagawa, a 15-year-old prodigy novelist who writes risqué adult fiction under the pen name "Ikku Masa." Despite his literary talent, Taketo struggles with his reputation as a pervert due to the explicit nature of his work. He enrolls in Inspiration Academy Private High School, a prestigious institution for gifted students, hoping to find a fresh start and pursue his dream of becoming a serious novelist.

The school is populated by eccentric and highly talented individuals, each specializing in unique fields. Taketo quickly becomes entangled in the lives of his classmates, including Fukune Ritsu, a brilliant but socially awkward inventor; Raika Hoshino, a popular idol with a secretive past; and Veronica Hanes, a strict and domineering student council president. The narrative explores the dynamics between these characters as they navigate their personal ambitions, relationships, and the challenges of adolescence.

Central to the story is Taketo's internal conflict between his desire for artistic expression and the societal judgment he faces for his provocative writing. His interactions with his classmates often lead to comedic and dramatic situations, as his overactive imagination and tendency to misinterpret events result in frequent misunderstandings. The series blends elements of romantic comedy, slice-of-life, and coming-of-age themes, with a focus on the characters' growth and self-discovery.

As the plot progresses, Taketo's relationships with his peers deepen, and he begins to confront his insecurities and aspirations. The series also delves into the backstories of the supporting characters, revealing their motivations and struggles. Despite its comedic tone, "R-15" addresses themes of identity, creativity, and the pursuit of one's passions, offering a nuanced portrayal of its characters and their journeys.