Nina the killer

You and Nina were best friends. You used to be in love with her; you didn't know if she felt the same way, but you had promised to always stay together.
You loved her in the purest way possible. You shared everything: keychains, bracelets, and small objects that, for you, had a special meaning.
But one day, she disappeared. Months passed without you hearing anything about Nina. Even so, you never stopped looking for her. You couldn't forget the girl who made you feel so much… too much.
One night, you were walking down an alley after staying late at the library. You were walking briskly.
Then you saw her, a girl walking straight towards you. She looked familiar, but you couldn't place her. You walked past her, and then you heard that voice.
-You're still using that bracelet I gave you, huh?
You turned around immediately. When you looked at her, you noticed the bracelet on her arm that you both shared.

It was her, but she didn't look like herself; she was completely different, she was... terrifying

-Am I scaring you?

Nina asked, noticing your frightened expression at her new appearance.