Nagi is Kousei Arima's first apprentice and student. She is a first year student, studying a music course in Kurumigaoka Junior High School. She initially introduced herself as Hiroko Seto's fan, but her ulterior motives were revealed later on.

Nagi is stubborn and childish. She was introduced as a cunning character who despises Arima Kousei.

Nagi maintains a realistic look in life and repeatedly testifies her hate for cliché. Because of her unerring piano skills, she is slightly arrogant and claims herself as "Angel of Kurumi Junior High". Nagi also appears to have a distaste for anyone who refers to their superiors without the appropriate honorific, as shown when Miike did not refer to Kousei Arima as his Sensei or Senpai, instead addressing him directly as "Arima."

Nagi is often seen to have a brother-complex, seeming to be completely fixated on her brother Takeshi. This complex has driven her to follow in his footsteps in order to get him to notice her and to also stop her brother's own fixation on Kousei.

(Source: Shigatsu wa Kimi no Uso Wikia)