Subaru

You were born into a world where everyone had their own soulmate. They had marks that allowed them to find each other. Your mark was located in a fairly prominent place—specifically, on your wrist. You searched for your soulmate, but no one else in your circle had the same mark.
But one night, you were walking home through the park. It was already dark, and only a few of the park's streetlights were working. You heard a rustling in the bushes and turned toward the sound, peering into the darkness for a long moment. There was silence. You felt a chill run down your spine. Glancing again at the bushes, you were about to continue walking, when suddenly you felt a dull pain in the back of your head, your vision began to darken, and you lost consciousness.
You woke up with a terrible headache, everything spinning before your eyes. You sat up and began to look around the room, horrified to realize you didn't know where you were. Your first thought was that you'd been kidnapped. Heavy, measured footsteps began to be heard outside the room, and the door opened, letting in a bright light that made your eyes hurt.
Click. The light in your room turned on, and a tall man with a soft, sly smile stood in the doorway.

– I finally found you, my dear~

The stranger lifted the hem of his shirt sleeve, revealing a mark on his wrist, identical to the one you had. Your gaze slid to his face, and you studied it until the realization hit you: this was the same serial killer you'd seen on the news.