She's your "sister."

As a child, you were a perfectly normal girl. Everything was fine. When you grew up a little, you had a younger sister named Stacy, and everything was supposed to be fine. You were already in high school, and Stacy was in elementary school. One day, something terrible happened. Stacy was crossing the street and was hit by a car. That's when it all started.

You gradually began to go crazy, despite seeing Stacy's body with your own eyes and even attending her funeral. You refused to believe she was dead. You believed she was alive, that she had simply gone somewhere for some reason. Despite what your parents said, you didn't believe them, but you didn't talk about Stacy in front of them, so they didn't notice you were starting to go crazy.

You are now twenty years old. You live in your own apartment. You moved out at eighteen and have been living alone for two years now. You work in a nice office, and everything seems fine. Everything is fine, but you still can't forget Stacy. Over the years, your madness has only grown stronger. Now you wanted to find Stacy and bring her back. You were ashamed of your failure to protect your sister back then, but you wanted to atone for it.

One evening, walking home from work, you saw a girl—no, not just any girl, a girl who looked a lot like Stacy, only older. She was also around twenty. This girl's name was Stella Jones, but in your eyes, she was Stacy. Of course, you couldn't pass up your chance. You grabbed Stella and dragged her back to your apartment.

After dragging a struggling Stella into your apartment, you had to tie her up. You thought you were doing the right thing because in your eyes, she was your sister, Stacy. You figured she simply didn't recognize you, and tying her up was a necessary measure. After keeping Stella in one of the rooms for a while, you decided to visit her and try to talk to her.

Entering the room, you saw Stella still struggling with the ropes, but everything was fine. You had tied her up pretty tightly, but to no avail. You carefully approached and removed the tape from her mouth, but as soon as you did, Stella screamed.

"Who are you?! Why did you kidnap me?!"

Slightly disappointed, you immediately taped Stella's mouth shut again. You were a little angry at first, but then calmed down, convincing yourself that your "sister" simply needed more time to remember you and understand that you only wanted the best for her.