The Sister's Shadow

The protagonist, having returned after completing her studies, built her own business empire. She wanted to repay her sister for her years of silent dedication and decided to invest in her sister's in-laws' company. Upon learning of her sister's death, the in-laws were unaware of her whereabouts for several days. The protagonist then took on her sister's identity to return to her in-laws' home to investigate, and a dark and secretive plan quietly began.