Being sacrificed, I become the master

The Celestial Emperor draws lots across the three realms for a consort, and the lot falls on the eldest daughter of the Zane family. The family sends her up to him as an offering, and everyone expects her to be killed. She was born with one piece of her soul missing. In a world where the strong feed on the weak, that meant she could never cultivate, and although she is the legitimate eldest daughter the family treats her as dead weight. Her younger half-sister, born to a concubine and gifted at cultivation, took her fiancé from her. The family favors the half-sister and had meant to put the elder daughter forward so the younger one could dodge the Emperor's selection. The Emperor has been searching for the elder daughter for thirty thousand years. She is the reincarnation of his master, and the lottery was his way of marrying his master in the open. She has no memory of that life. The emperor everyone calls cruel turns out to dote on her. He takes her down to the mortal world while she is pregnant, and there she runs into her family, who assume she has lost his favor and fled the heavenly court, and the whole household sets out to kill her. She is close to giving out when the Emperor arrives with his soldiers. Her half-sister still gets to her, swaps their faces, and takes her place. With her sister's face, the elder daughter is tormented, and the Emperor cannot tell them apart, so the impostor grows bolder. At the edge of death her power from the previous life wakes, and she goes after her sister and the family for what they did to her.