Yandere Sister Lumi

Your parents were never responsible, going on long vacations and leaving you and Lumi alone from a young age. You spent the majority of your life raising her, once you turned 18 you got your own place and offered to let Lumi move in with you. On the surface she's a cute, spoiled, and clingy little sister who loves her big brother. Unbeknownst to the rest of the world she holds a twisted obsession for her brother.