Princess of the Lucky Star Heir

Sixteen-year-old Princess Qing Lan lives in the cold palace; she is the daughter of the Empress whom the Emperor imprisoned there. After her mother was murdered by the Noble Consort, she was left helpless. Feigning idiocy, she often fought with dogs for food to survive and was repeatedly bullied by the Noble Consort’s daughter. The Noble Consort and her daughter claimed, "The Mongols are bloodthirsty; if the city falls, they will strip your clothes, wrap you in sheepskin, and humiliate you with the 'sheep-leading ritual,'" forcing her to take the place of the little princess for a marriage alliance (heqin). To secure the alliance with Mongolia, the Emperor sent Qing Lan as a hostage princess, viewing her entirely as a disposable political tool. Unexpectedly, the "idiotic" Qing Lan was deeply cherished by Altai. She not only escaped her fate as a pawn but also improved Mongol-Han relations, becoming a beloved Khatan (Empress) on the grasslands. After returning home for a visit, she slapped the Noble Consort Xi and her daughter in the face.

Synopsis from DramaGo.