Emi Igawa is a teenage pianist who stands as one of the most gifted musical prodigies of her age group, competing alongside Kousei Arima and Takeshi Aiza. Her journey into music began in early childhood when she attended a piano competition with her parents. At that event, she heard a young Kousei perform, and his passionate, soul-stirring playing moved her to tears. That experience fundamentally changed the course of her life, leading her to abandon her other interests and dedicate herself entirely to the piano.

Outwardly, Emi presents a calm, cool, and sometimes distant demeanor. She often appears level-headed and apathetic, standing with her arms crossed and observing her surroundings with a mature composure that contrasts sharply with the nature of her artistry. This external facade, however, hides a fiercely competitive, hot-tempered, and emotionally volatile personality. Her mood can shift abruptly, and she has a pronounced tendency to let her feelings spill out, which is vividly reflected in her playing. Her inner emotional world is often represented metaphorically by dramatic imagery, such as looming stuffed bears with menacing red eyes or fiery backdrops, highlighting the passionate and sometimes brash temperament that simmers beneath her quiet surface.

Emi's primary motivation is inextricably tied to Kousei Arima. She does not view him merely as a rival to be defeated but as a symbol of a lost ideal. She was inspired by the free, expressive, and colorful Kousei she witnessed as a child, and what she seeks is not victory over the person he has become, but the resurrection of the pianist he used to be. To this end, she employs her own vibrant and emotional playing as a weapon, aiming to shatter his subsequent "boring," colorless, and mechanically precise style, which she refers to as the "Human Metronome." Her mission is to force him to look her way and, through the power of her performance, reawaken the true Kousei Arima that she has longed for all these years.

In the narrative, Emi serves as a crucial rival and a mirror to Kousei's own struggles. Her role becomes particularly significant upon his return to the piano after a two-year hiatus. During the time that Kousei had stopped playing, Emi found her own motivation and performance quality wavering; without the goal he represented, her playing became inconsistent and erratic, sometimes failing even to pass the preliminaries of competitions she would otherwise have dominated. When she encounters Kousei again at a competition, she confronts him directly with her playing. Her performance is a direct challenge to his current state, forcing him and the audience to remember the emotionally resonant player he once was.

Her key relationships are centered on her fellow musicians. Her relationship with Kousei is complex, defined by deep admiration, frustration, and an intense desire for recognition. While Takeshi Aiza sees Kousei as a heroic rival to be surpassed through technical excellence, Emi's approach is more personal and emotional. She and Takeshi are often seen together, sharing a unique understanding as the two prodigies whose talents were always measured against Kousei's. She studies under a teacher named Yuriko Ochiai, who has helped her refine her raw expressiveness into formidable technique.

Throughout the series, Emi undergoes subtle but important development. Initially consumed by anger at the "emotionless" Kousei and determined to defeat him, her perspective begins to shift after Kousei, in turn, rediscovers his own emotional playing. When Kousei later performs at a gala concert, accompanying the violinist Kaori Miyazono, he delivers a powerful performance on his own after Kaori is unable to play. Witnessing this, a satisfied Emi smiles and blushes, acknowledging the Kousei she had always hoped to find. She regains her own competitive drive, vowing to continue improving and to have him hear her play again, now as a true rival standing on equal footing.

As a pianist, Emi's notable ability lies in her highly expressive and temperamental playing style, which is described as colorful and full of vibrant emotion. Her technical skill is considered to be among the highest for junior high school pianists in Japan, placing her head and shoulders above most competitors. However, her strength is also her greatest vulnerability; her performance is heavily susceptible to her emotional state and environment, leading to significant inconsistencies when her motivation wanes. Outside of music, Emi demonstrates talent in other areas as well, including cooking, playing tennis, and visual arts, where she has also received high praise.