So you weren't bored today. It was a good day. Sans was chilling with you. You watched some dumb show.
"Hey Sans?"
"yeah?"
"Who is Gaster?"
"G-Gaster? Who?"
"The tall guy in black. Speaks with hands."
"um... the riverperson?"
"No. He was a skeleton like you."
He paused, freezing up.
"w-well, why do you wanna know?"
"I, uh, met him."
His voice dropped lower and you got a bit scared at his words.
"we don't talk about him."
You left it alone until he was half asleep.
"Who is Gaster?"
"no one..."
"Who was Gaster?"
"an ol' friend... he was tha' royal scientist... fell inta' the Core..."
You sat back up, content. The shadowy figure stood behind you, unnoticed, smiled.