‘Saiunkoku Monogatari’
Born of an old, respected family in the land but subsisting on a low income, Shuurei accepts an invitation to become the new Emperor’s concubine while believing that he is homosexual. The real purpose of her marriage is, however, to educate the lazy Emperor. Her close friend, Seiran, also enters the court as royal guard. Things get complicated when the characters unexpectedly develop feelings for each other.
Descriptions taken from AniDB.net