Irene Tylon, who was reincarnated as a fallen noblewoman in a novel, is taken in by the Duke of Casaros and meets Atan Casaros, the duke’s illegitimate son. In the novel, Irene becomes a villainess who bullies Atan, her younger stepbrother, and is ultimately killed by his hand. To avoid that fate, Irene tries to keep her distance from Atan—but seeing him isolated in the mansion, she can't help but reach out to him. Before long, Irene and Atan begin to form a bond like real siblings. However, Atan, who was once just a cute little brother to Irene, grows into a handsome young man with an intense obsession for her... “Please... don’t leave me...” Will Irene be able to withstand Atan’s twisted, obsessive love—!?