She is the older sister of Nitori Shuuichi, in fact, Shuuichi as a girl looks almost identical to her older sister. Her personality is seen as the opposite to Shuuichi's calm and quiet demeanor, often being loud and outspoken. She also sees Shuuichi's crossdressing supposedly as a sickness, and that it isn't something that she should be doing, thinking that it is only a phase. She acts out of concern for her sister, even if it isn't shown outwardly.
She is shown throughout the series, usually as a counter towards Shuuichi's crossdressing, and being very vocal against him doing so, as she perceives it as weird, and something that hinders his future. Although seemingly harsh towards Shuuichi, she is known to care deeply for him. She starts dating Riku Seya midway through the season and is more calm and collected then Maho. She at first compares herself as looking like Shuuichi, but Riku corrects her, saying that he looks like her, not the other way around.
She helps Shuuichi get closer to Anna Suehiro, and when they start dating she tries to make sure that Shuuichi won't crossdress again, as she feels that Anna is normal and what he does is weird. Anna assumes that Maho would not want to be friends, but this is shown to be untrue, and they get along after Shuuichi and Anna get back together.