Akki no Koukyuu Kaen

Hu Linghua is the "evil princess" feared by everyone. Her true identity is the polar opposite of an evil woman, with a lovely face and pure personality. No one knows this... or so they thought. Until she received a secret mission from the Crown Prince, Hakuren. "Become my consort and my younger brother," Linghua ordered, and began living a double life as both the "favorite concubine" and the Crown Prince's "younger brother" --!?

(Source: Kadokawa, translated)