Kasen Koushu Yawa: Sono Reijin, Koukyuu no Yami wo Kiru

Legend has it that the first emperor founded the country with the help of celestials. One day, a young prime minister candidate, Li Hakukei's (Li Bo Qing ), visits Shou Meika (Xiang Ming Hua) the mistress of a tavern, who is touted as a "beautiful woman of unparalleled beauty."
In fact, Meika's true identity is Princess Kasen (Hua Xian), a princess rumored to be the late emperor's lost child. In order to protect the country on the brink of extinction and the young next emperor, Seishi (Shi Zi) Hakukei has offered Meika a deal.

I don't give a damn about the country, but I want to protect cute Seishi. Wishing to do so with all her heart, she accepts Hakukei's offer, suspicious as he was.

Source: Mangadex