Yuzuru Nishimiya, little sister of Shoko Nishimiya, was raised by their mother to be a boy in appearance, personality, and presentation. Yuzuru is not a transgender person, but is gender non-conforming because that is how their mother wanted them to be; to be thought of and accepted as a young male in all aspects of their life. Yuzuru knows that she has a gender identity of that of a female, but is fine with always dressing as and giving the appearance of a boy.
When Yeako Nishimiya found out that her daughter, Shoko, was a deaf/mute child, she decided that Shoko would always be ( supposedly ) vulnerable and unable to take care of herself. She thought the best way to address that was to raise Shoko to be a boy, with a boy's attitudes and personality, one who would be able to fight for their place in the world. However, Shoko steadfastly refused to dress as a boy, have a boy's personality, or present in any way as a boy. She consistantly resisted all attempts of her mother to ingrain a male's gender expression onto Shoko. Shoko was ultra-feminine in appearance and presentation to begin with, and preferred to stay that way for the rest of her life. Therefore, when Yeoko was pregnant for a second time, and gave birth to another girl, she vowed to raise that child as a boy, in order for them to be the one to take care of and protect Shoko. To help accomplish that, she chose a decidedly male name for her second offspring---Yuzuru. Although it seems that Yuzuru had little choice in the matter of presenting as their opposite gender, they seemed to go along with the role that their mother had laid out for them with little or no objections. And Yuzuru did take seriously their role as the Protector and Guardian of Shoko, all the way through their teen years.
Yuzuru became interested in photography at an early age. They were fascinated with a camera and how it worked. Yuzuru, through the years, became an excellent self-taught photographer, and was able to win a prize and award in a photography contest that was sponsored by the local newspaper.
Yuzuru, for a time, dropped out of middle school for whatever reason. They became somewhat depressed, and only had interest in their photography endeavors. Even then, Yuzuru's photography took a uneasy twist, in that they began only taking pictures of dead animals or dead insects. Later, it is shown that Yuzuru did this so as to show the gruesome pictures to Shoko, in an effort to dissuade her from committing suicide. However, about the time that Shoya had begun dating Shoko, and after Shoya had recovered from his fall from the third story balcony, Yuzuru was convinced to return to school. But despite being raised as a boy, the school insisted that Yuzuru wear the female school uniform, a sailor fuki (sailor suit) while at school. Thus, in a real paradox, the teen raised as a boy takes on the appearance of a cute, pretty, attractive teenage girl, at least at school ! Yuzuru even began to consent to wear her girl's school uniform at home and occasionally out in public !