Read Genius Doctor: Black Belly Miss Manga:
While escaping from her crazy scientist grandfather, young and genius Xi is killed in an explosion and is transferred into another world, straight into a body of a dying girl. Grasping onto hope, in exchange for a promise to be saved Xi frees a mysterious man... and now she is the eldest good-for-nothing daughter in a Duke's family!
Her new grandfather is a doting old guy, her uncle is more.. crippled and she herself is despised for not having a spirit familiar. Moreover, her fiance is the second prince but her family doesn't seem to have a good relationship with the Emperor. And her enigmatic savior - why doesn't he wish to leave her side?