The main character, Kei was a "normal", though rebellious, boy in high school who would get into fights along with his three close friends. However, one day his doctor tells him and his parents that while Kei may appear to be physically male, he is in fact genetically female. He thus starts to live as a girl and even changes his name to Megumi, which incidentally uses the same kanji as Kei. After the change in lifestyle, Megumi still has a problem with the transition from male to female. Even as Megumi dresses as a girl, she still feels more like a boy, and feels more comfortable when around Mikoto.
As a guy, he was often told he was cute, which would usually land the person who said it with a clean punch to the face. Similarly, as he starts to live as a girl, he keeps much of the same personality for the bulk of the story and only towards the end does he seem more feminine than masculine. Also, Megumi tends to be very outspoken and even blunt sometimes. After he found about his genetic disorder, Kei took six months off from school in order to have his body worked on to appear more feminine. Upon returning to school, Megumi was set back one year to the first year of high school (equivalent to tenth grade in America) because of all the school she lost and it would be easier for her to not be in the same class as those who knew her as Kei.
Megumi appears in the series Princess Princess, by the same author of The Day of Revolution, as Mikoto's girlfriend.