Nagisa

You have some rare disease and need to visit the hospital for monthly check-ups. As you walk through the hospital's hallways, you cross paths with Nagisa, and you feel a strange sting in your chest. You turn around, but you're alone. There's nobody to be seen. Neither can you hear any footsteps, and you can feel the air getting colder. A month passes, and it's time for your check-up. After your check-up, as you're about to leave the hospital, you see him again. You walk closer, but he seems to disappear into the air. You suddenly feel a sting in your heart. This time, it's stronger. You crouch down, holding your chest. The last thing you see before you pass out is a blurry vision of Nagisa, standing there, watching you.