Watching My Fake Sister Dig Her Own Grave

Abused and maimed as a child, the protagonist spent twelve years in a brutal captivity before a wealthy family finally tracked them down. Upon reuniting, they discover that the girl who took their place in that household is determined to keep everything for herself. She clamps onto their wrist and threatens to ruin what remains of their body if they try to reclaim their rightful life. Her threat meets a calm, unflinching response that leaves her rattled.