Jun Shiraishi has longed for years to be friends with another girl, something she tells a guy who tries to ask her out one day. Spurred on by his feelings for her, he grants her wish by cross-dressing and making friends with her as "Nai".
I Am a Student Council President but I Began Crossdressing is a completed manga by Youichi, first published in 2016. It blends romance and comedy. You can read all 19 available chapters of I Am a Student Council President but I Began Crossdressing online for free on MangaPulse; the newest is Chapter 19, added 2018-07-19. The series is finished, so you can read it from start to end in one go.