Yagate Kimi ni Naru

Synopsis

As the student council look for someone to write a script for their play, Sayaka approaches Yuu, who had Koyomi in mind but didn't bring it up out of concern for Touko, and tells her to look into the student council president of seven years ago. Unable to find any relevants documents from seven years ago, Yuu learns from both Rei and one of the teachers that the president back then was Touko's older sister, Mio, who died in a traffic accident before she cound perform at the culture festival. Realising that Touko has been trying to imitate her sister, Yuu tries to convince her not to force herself to do the play, but Touko refuses, feeling she can't let go of what makes people consider her as someone special. Stating that she can't fall in love with either side of Touko, Yuu promises to stay by her side and help with the play.

(Source: Yagate Kimi ni Naru Wiki)