Igawa, Emi

It was shown that prior to the storyline, Emi and Takeshi are sitting together complaining about the "emotionless" Kousei Arima after losing to him in a piano competition. The rest of the crowd points out that Takeshi and Emi are head and shoulders above the rest of the competition, which makes Kousei all the more invincible for beating the two. While Takeshi sees Kousei as a rival that pushes him to greater heights, Emi has a different motive. She was originally inspired by Kousei's passion and pure innocence during his first performance, she decided to learn piano under Yuriko Ochiai for the sake of expression. Over the course of the story, Emi seeks to oppose the "boring" playing style of the old Kousei in hopes to find the "true" Kousei once again.

(Source: Shigatsu wa Kimi no Uso Wikia)