Gaster had been cast out for his experiments with the mortals. The higher-ups had wanted weapons for the demons, so it was exactly what he tried to do, using his blood to try and create more Exterminator Angels like himself. Unlike the higher-ups, Exterminator Angels could not reproduce, so the 500 that had been created were all. Once he was found out, he was cast to Hell, just like master Lucifer. Knowing that the King was the cause of the death of most Exterminator Angels, Gaster managed to escape to the mortal realm, damaged. His face was scarred, and his wings were now useless, but despite what happened, he continued to try and create new Exterminator Angels, even when he was cast away once more to the Underground with the monsters. He disguised himself as a skeleton monster and added himself into their ranks, eventually becoming the Monster King's Royal Scientist. Trying to turn dying monsters into Angels ended in melted abominations whose souls were neither demon nor angel. They were trapped in Purgatory. But with the human child dying... he thought they would be the perfect test subject. Acting as their doctor, he subjected Chara to his blood.

XXX

Gaster did not foresee Asriel absorbing their soul and altering himself as well. Nor did he expect them both to die. Last of all, he didn't expect the human to become a demon or Asriel to become a demonic little flower. Perhaps he needed to take a different approach, try a living soul, rather than a dying one. That was where the orphan skeletons came in. Sans and Papyrus. They gave him more time to continue the injections, the experiments. Trying to make them show angelic properties while they were still alive. Gaster never thought he would be able to see the end result. Eventually, the higher-ups found out of his escape, and he was punished into Purgatory. Trapped in endless darkness with the souls of his trapped experiments screaming at him for his sins against them. On occasion, he met the child, doomed to be possessed by the failed experiment Chara. Sometimes, he had the pleasure of speaking to the demon he created himself. Now he was speaking to the failed experiment Sans, the second demon of his making. He did wonder... wherever did the other one go?

XXX

Sans felt sick. Their soulling trembled in response, and Alastor wrapped his arms around them. "So... do tell me... where is the other one? Papyrus?" Gaster asked. Sans had been certain that Papyrus wasn't touched. Papyrus had been... if Sans was in Hell, where the hell was Papyrus?! "Hm, you don't know, do you? Perhaps... the experiment was more of a success than I thought?" The fallen angel mused. "get me outta here... please get me... i can't be here anymore..." He felt like his soul was shattering. Not only did he fail to protect his baby brother, but there was a possibility that they were on opposite sides of an ancient war. Sans was whisked away from Gaster immediately and brought back to the hotel. He now had an incentive to be redeemed and go to Heaven, but what about Alastor and Anthony? Would they follow? What about their child? What if Papyrus really was gone for good, and he left the people he cared about for nothing? But what if he was there, waiting? "It's alright now..." Alastor reassured. Before Sans realized it, they were in his room and on his bed. "You're safe now, Sansy..." His boys were cuddling him, reassuring him... he would be alright...