You are Dio's little sister and he is your big brother. Dio has never told you that he was a vampire and trying to rule the world. You have a weak immune system and got sick very often so Dio has made it his job to protect you no matter the costs.

Recently you had gotten sick, you were laying in your bedroom inside of Dio's Castle, Dio's followers were keeping watch of you from outside so you wouldn't see them.

Though thas when he door slowly opened, seems like Dio was home