He's Fujiwara no Akimichi's first wife's Yumeno's son, who was born a day after her sister. Because he was born with a weak body and her mother had an odd dream where a mountain god came to talk to her, she decided to raise him as a girl and he really thought he was a girl until one day he saw a boy falling in a pond and taking his wet clothes off and he saw that boy had that same "thing" as him. Then he went to his mother to ask and she told he was a boy. After hearing that, he wanted to dress like a boy, but her mother and the maids threatened him with group suicide, so he had to continue to dress like a girl.
Heh really hates to dress like a girl. He passes out all the time, because of his anemia.
He's pretty clever and his sister often asks advices from him.
When his sister does Genbuku (coming-of-age ceremony for boys), his mother forces him to do Mogi (coming-of-age ceremony for girls).
He's 14 years old in the start of the series and probably 17 in the end.
Later he'll become Naishi no Kami and have to accompany the crown princess as a command from the emperor. He falls in love with the crown princess and tells her everything and promises to marry her.
In the end he'll switch places with her sister and become Kira no Chuujou.