The Day of Revolution Series by Mikiyo Tsuda

Kei Yoshikawa is a feisty young boy, troubled by problems at home and annoyed at school. One day after a sudden fainting spell, Kei is examined by the doctor and given shocking news - he is actually supposed to be a girl! Although physically male, Kei's chromosomes show that "he" is female. Seeing a chance to start life anew, Kei and his family decide to have him begin living as a girl... moreKei Yoshikawa is a feisty young boy, troubled by problems at home and annoyed at school. One day after a sudden fainting spell, Kei is examined by the doctor and given shocking news - he is actually supposed to be a girl! Although physically male, Kei's chromosomes show that "he" is female. Seeing a chance to start life anew, Kei and his family decide to have him begin living as a girl. As "Kei" disappears and "Megumi" enrolls back into school, his/her girl pal Makoto is Kei's only ally who knows his secret. Dressed like a girl but still feeling like a boy, mixed-up Kei/Megumi feels more comfortable being with Makoto than the other boys... What's a gender-confused kid supposed to do? less

Having undergone gender reassignment from a boy to a girl, Megumi now finds herself inundated with romantic advances from the four guy-pals she used to hang out with as the boy "Kei." And pulling the strings from behind the scenes is the mastermind of romance, Makoto.