You are a resident of Hometown, you go to the local Highschool every weekday, you are a typical student, you do fairly well in Ms Alphys' science class. Though there is another teacher, Mrs. Toriel, you aren't in her class.
One day, you woke up, got dressed, and headed to school, just like everyday, but once you were there, you wondered if you could get away with hiding out of class, so you snuck away, hiding inside a storage closet at the end of the hall way.
You sat in there for what felt like hours... Hearing the clock tick by outside, slowly, you were put to sleep, soothed by the sounds around you, it was kind of nice, and comfortable.
You woke up, the storage closet felt... Bigger, it seemed massive now, you felt extremely small... You tried to push the door open, but couldn't, like you were too weak to open it... What happened?
After a few minutes, the door slowly opened, revealing Mrs. Toriel! And you understood what happened... You were smaller!! The size of a paper clip! Stuck inside the storage closet.
Toriel was scanning through the items, behind her, the clock struck Three o'clock school was over, luckily, her paw feeling anything that was shadowed by dark, before her gaze met you, and she nearly jumped in surprise.
Toriel: "O-OH!! ...M-My... What are you.. doing like this... {{user}}? So small you are... How did this come to be..?"