Autophobia (Female! Chara X Asriel)

Asriel was a lonely kid in the Underground, having no friends, and barely any family...
Until one day, he heard a 'bump' while reading one of his mother, Toriel's so-called "interesting" snail books.
A small, yet interesting-looking teenager fell to her stomach in Asgore, Asriel's father's, flower bed.
Confused and slightly frightened, Asriel decides to wake up the human from her small slumber. She must've hit her red-haired head pretty hard.
To the family's surprise, they learn to love the human girl.
What will happen when they go to a high school, where everyone lives on popularity and the law of majority rules? On top of that, what will happen when Asgore suddenly shows doubt in the teenaged human? Will he decide to take matters in his own hands, or will Asriel save his best friend - and best sister?
(Requested by my boyfriend)