Nevertrust sans was a normal sans living in a pacifist route. One day in the city on the surface, human was murdered by another human. Sans took dead man's soul and kept it secret. Few months later, Chara got bored and tried to manipulate with the weak bodies of patients when Frisk was at the hospital. Chara then possesed a weak monster. Chara immediately rushed on Frisk stabbing them with scalpel. Frisk then got really weak and Chara possesed Frisk. And then, Chara started their pacifist-genocide route. After countless deaths including Toriel, Papyrus, Undyne, Alphys, Mettaton and Asgore, Sans lost fate in all humanity and the only thing to do was consuming the souls of the loved ones before Chara completely wipes them off the world. With his new power he teleported into void where he spends his time exploring the mystery of humans and monsters soul.