~Lusting~ Undertale X Reader Oneshots

{SMUT} Gaster X Male!Reader

warnings: reader is held (mostly) against their will and is not asked for consent, mentions of blood, sort of stockholm syndrome, gaster is a dick (and not in a good way)

read at your own frisk

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You sat idly on the cot in your small cell, sighing. Dim lights barely illuminated the small room, leaving the corners in darkness. A single door led to the bathroom, even smaller than the room you slept in. One wall was entirely glass, allowing you to see outside. Like your cell, though, it was dark and grim.

Occasionally- maybe once or twice a day- a tall skeleton would stop by. He was the only person you'd seen since your abduction in Waterfall. He looked intimidating, wearing an emotionless expression and a lab coat with clipboard tucked under his arm.

You only saw him when he was bringing food. He might write something down on that clipboard of his, muttering to himself, but you couldn't hear him through the glass. It was hard to read his lips, too, because he didn't have any.

Sometimes something new would happen, like you waking up with a bandage somewhere on your body. It seemed like he was either taking blood samples or injecting you with something- maybe both. You didn't feel out of the ordinary, though, except for the crippling loneliness from being trapped in a small room with no way to contact other people for what seemed like weeks.

One day, the skeleton walked up to your cell, muttering to himself. He had brought your breakfast not too long ago, hadn't he? Why was he back already? Maybe you were just that bad at telling time.

You heard a clicking sound. A section of the seamless glass separated and slid aside, leaving a doorway out of the cell. The skeleton stood in front of it.

"Well?" he said. "What are you waiting for?"

You weren't sure what to say. Was he letting you go?

"...Who are you?" you asked.

"This way," he said, ignoring you entirely.

Reluctantly you obliged, following him down the hallway and into a different room. Was this one of those tests he'd been doing while you were unconscious? If so, why was this time any different?

It was probably best to just play along for now. You had no weapons and no idea where you were. If you could gain the doctor's trust, maybe he would let you leave.

"Sit here," The skeleton motioned towards what looked like an operating table. You did as he said, panicking internally.

"This shouldn't hurt. You might even enjoy it," he said, strapping you to the table. Realizing you were still only wearing a medical gown, you blushed slightly, averting your eyes away from him.

He adjusted his glasses and pulled over a large machine and fixed it to the table. Then he grabbed a long tube from the side of it, slightly adjusting something on the end.

You could only think of one place something like that would fit on your body, but it seemed ridiculous. 

You were quickly proven wrong. The skeleton pulled the gown you were over your head, leaving you completely exposed. "W-what are you doing?" you said frantically, blushing profusely. Instinctively, you tried to cover yourself with your legs, but they were strapped too tightly.

He lowered the hose onto your involuntary half hard-on, strapping it around the base.

He stepped back, looking you over- whether to ensure the success of the "experiment" or just look at you, you weren't sure. His face remained stoic nonetheless.

Seemingly satisfied, he turned around and left the room. The door swung shut behind him. You laid there alone for a few seconds, but the silence was interrupted by the motion of the machine.

The rhythm of the device quickly brought you to full mast. You moaned softly, starting to thrust back, but the restraints were too tight. You couldn't even remember the last time you'd jerked off, and this was a welcome change of pace. 

Gaster watched the situation unfold from behind the one-way glass that separated him from you. While he'd calculated that this was by far the most efficient method, he hadn't expected it to be so... entertaining. Your moans and thrusts were amplified by the speakers in the observation room.

He began to feel a tightness around his crotch. A faint purple glow illuminated his pants. It had been awhile, hadn't it...? Maybe just this once.

Gaster unbuttoned his lab coat, his eyes fixated on your naked body. He watched you thrust eagerly as his pants fell to the floor.

He wrapped his hand around his cock and started to move it slowly up and down, his eyes fixated on you through the glass. A strong purple light shone on his body as he touched himself. Gaster closed his eyes and listened, hearing your moans and the wet sound of the machine as it jerked you off.

Your breath sped up and you started to thrust faster as your neared your climax. You no longer cared whether the skeleton was watching or not. He was going to get one hell of a sample anyway.

You moaned loudly as you came, feeling the tube milk you. Gaster huffed, grabbing a beaker from a nearby table as he watched you and quickly finished himself. He moaned with you- though only he could hear it- as his cum filled the beaker, leaving a fair amount of glowing, purple liquid in the bottom of it.

He sat back in his chair, sighing, and watched you come down from your high. You'd certainly exceeded his expectations for the first trial. Normally he'd wait before the second, but you still looked perfectly aroused.