Ritsu Enshū is a 15-year-old mathematics prodigy attending Inspiration Academy Private High School, an institution for specialized geniuses. He shares a notably close friendship with Taketo Akutagawa, standing as Taketo's most loyal companion within the series. Ritsu consistently defends Taketo's work against criticism, demonstrating his deep trust in Taketo's character and abilities.

A distinct behavioral trait emerges during ordinary conversations, where Ritsu experiences sexual arousal. To manage these reactions and restore his composure, Taketo employs a specific distraction technique: instructing Ritsu to recite the digits of the mathematical constant pi (π). This method effectively leverages Ritsu's intense mathematical focus.

His name, "Ritsu Enshū" (円周 律), holds linguistic significance, directly referencing pi (π) in Japanese and aligning with his mathematical identity. This naming follows a series pattern where characters' names often connect to their fields of genius.