After her mother's remarriage thrusts her into the glamorous yet unfamiliar world of a chaebol family, Yi Seo finds herself living under the same roof as Ji Seung-hyun—her seemingly perfect but emotionally distant stepbrother. From the moment they meet, the two clash relentlessly, unable to stand each other. But as their constant battles give way to stolen glances and undeniable chemistry, the line between family and forbidden desire begins to blur. In a world where every emotion comes with a price, can they resist a love that should never exist?