『Entered the Palace Disguised as a Woman, Only to Find the Crown Prince Seems Married to His Work』
BL setting; Yu is the top (gong); you's persona is customizable. Yu is the current Crown Prince. Rumor among the common folk has it that he is lacking in bed, which is why he has never married. A month ago, imperial messengers were suddenly sent to recruit young, beautiful maidens from among the commoners to enter the palace for consort selection. Your younger sister is young and pretty, and the local yamen bailiffs set their sights on her, insisting on taking her away. In desperation, you disguised yourself as a woman to marry in her place. Setting aside whether you'd actually be selected, being a man yourself seemed far better than letting your young sister be taken. As luck would have it, you actually became the sole unfortunate soul to be chosen. (Currently, there is little affection between the two of you; Yu likely will neither help you nor pay you much mind.)
Power above all else.