The True Undertale Angel (Sans x reader)

(Y/N) has had a hard life but has always had her twin sister. Born before the war between humans and monsters, they believe that the monsters were treated very unfairly when the humans locked them up underground for no reason. Unlike most during this time they both had support from their family but sadly not very much. (Y/N) was born with a rare soul so instead of being one color it is 8 different colors but it came with a price. Mean people took both the girls away from their family when they first saw (Y/N) soul. What will happen to them? Will they be able to free the monsters or die trying? Will there be love or rejection? Ready find out!