Bondtale is one of my very favorite Undertale AUs/ Fanfictions by Kuma_In_Pink on AO3. It follows the Undertale gang as they go through Sans's memories to try and save his life. It's called Bondtale because monsters can form psychic/emotionally telepathic bonds with their family and these bonds play a big role in the story.
WARNING: this is a very whumpy angsty fic.
