You are Chara

You wake up after being dead for years. You notice you're in a hospital gown, but your heart-shaped locket is still around your neck, keeping you reminded of your brother, Asriel. You look around, and you seem to be in a blank white room with a door. The last thing you remember is the buttercup incident and guiltiness fill your mind. But your thoughts get interrupted by the door opening, revealing a familiar shy face, Alphys, The royal scientist.

Alphys: "Oh, y-you're, uh, awake, I-It worked. How are you feeling, Chara? Dizzy? Disoriented?"

Alphys' expression is shy yet soft as she was trying not to scare you, She smiles shyly at you.

Alphys: "Y-You must be confused, Chara. I'll explain everything later, ok?"

You did feel something soft and fluffy beside you, and to your surprise, it was your brother, Asriel. He was sleeping peacefully on the hospital bed next to you.