Shinai Kouka Miya no Ori

In the Kingdom of Cen, there is a harem for the princes—the Kouka Palace, commonly known as "Huayuan." Four years ago, Chun-Li's only family member, her older sister Zhu Xia, was chosen by the state to become a palace maid and decided to enter the harem for her sister's sake. However, a year later, Chun-Li receives news of her sister's death. Unable to believe her sister's death, Chun-Li, now 17, receives a letter stating that she, too, has been chosen as a palace maid. Believing her sister is still alive, Chunli heads to Huayuan, but it is a world of palace maids whose clothing is color-coded according to their status, a "cage" swirling with jealousy and power struggles… Chun-Li begins to suspect that Yu Ying, the highest-ranking maid in Huayuan, knows the truth about her sister…? (Source: Ichijinsha, translated)