A tall figure stood waiting in the center of a small, barren room. The figure was a man who wore a hooded black cloak and a dark brown undershirt, along with a pair of long black boots. He knew not exactly what he waited for, but he waited all the same. As was the result of the experiment that cost him not his life, but his existence. Across every timeline and universe, there would not be a single soul who knew his name; W.D. Gaster. The few who had the chance to see him had failed to maintain their sanity, resulting by their community in either imprisonment... or death.
Sighing, he slowly pulled off his hood to reveal his skeletal face. His eye sockets were slightly misshapen, even for functioning the way a human eye would, and his left and right eyes each had a narrow crack running upward and downward respectively. His mouth looked not like a skeleton's jaw at all, but rather like a human mouth, with a flexible slit allowing him to speak.
After about ten more minutes of waiting, he heard footsteps coming from the other side of the gray door that connected the real world to his prison. Glowing white pupils appeared within his empty dark eye sockets, then faded just as quickly. The door creaked open, and a small human emerged from it, looking around the age of twelve. They had short, light brown hair and narrow copper eyes. They wore a blue and purple striped sweater and jeans, with worn-out leather boots covering their feet. The human hesitantly stepped forward into the room, looking inquiringly at Gaster. They reached a hand out and tried to touch him, but their hand phased right through him.
"That won't work. My body lacks any physicality." He said to the human, receiving a confused glance in response.
Of course, Gaster thought, I must sound like gibberish to them.
Considering all other options first, the human mustered the strength to summon their soul, and used its energy to try and interact with Gaster.
At that moment, Gaster figured it out. This is what he had been waiting for. The human's determination was what would give him the strength to be free from this prison. Letting out an unintelligible laugh and startling the child, he used his newfound strength to finally escape the room with the snap of his bony fingers. It was finally time. The experiment had begun.