Mark was as cautious as he was excited. He never has suspected such a thing would ever happen to him in his lifetime, yet there he was.

"Why exactly do you want to do this?"

Before him stood a barely dressed girl made of a gelatinous substance. A silk robe, loosely hanging from her shoulders, was the only thing preventing him from seeing her in full glory. Almost a whole head shorter than him, petite, but curvy - just his type. The whole slime thing weirded him out, but seeing her enticing shapes, he was slowly getting used to it. She replied:

"I am almost two hundred years old. I've lived through death and conquest and I've dealt death and conquest. Assumed the role of a carnivorous monster that was given to me. After all that time, still I live. So I've decided to explore, what more is there to life. And the world of sex seems like a big treasure trove of hidden pleasure I haven't known before."

She pulled the robe ever so slightly, causing it to finally slide down her shoulders, exposing her full breasts. They behaved the same as human breasts would, with the difference of being a tiny bit more bouncy.

"Be not deceived. I might look like a girl, but in reality it's just a shape I assume. I want to be sure you realize that before we proceed. On the flipside, I can control the shape, color, texture and temperature of my body, so I have a lot of potential to give you the perfect pleasure."

She glanced at the front of his trousers.
"You seem already excited" she said, smirking. "I wonder how much more excited you can get..."

Her robe slid completely off her, revealing her wide hips supporting a slim waist. What he saw before him was the sexiest body shape that his twenty years old mind could imagine. He felt himself getting rock hard, to the point of the walls of his penis hurting slightly with arousal.

She pushed him onto the bed, her wet-feeling, slightly cold hands on his chest didn't leave the best impression. But, as she took of his shirt, he felt both of these sensations disappear, eventually ending up on a feeling of a hot bath, but not hot enough to burn. She smiled even more after getting his dick out of the trousers.

"Seems like I'm lucky today, you're quite a hung specimen."

Once fully naked, she kneeled above him while he laid on the bed, her intent being - do everything to give him a sex experience of a lifetime. He relaxed his whole body as she started impaling her vagina with his dick. The feeling was amazing right away, but somehow it kept getting better over time, as she was reading the slightest changes in his facial expressions and adjusting accordingly. He grabbed two handfulls of her breasts, and they felt better than he could have hoped for. If this wasn't heaven, he didn't know what was. 

He came barely a minute after, absolutely unprepared for the barrage of pleasure she gave him. He saw his load float in her translucent belly, then it started slowly disappearing.

"Huh? Why is my sperm disappearing?"

"Do you need it for something?" She laughed. "I figured, since it's already inside me, I might as well snack on it. I'm a carnivorous slime, I eat by dissolving things."

"Ah, makes sense."

She glanced at him with a joyful expression.
"Of course it does. Ready for a second try?"

"Oh yes please" he said, twitching with excitement.
She started riding him again, going lower and lower with each bounce as he seemed to enjoy it.

"Seems like he enjoys feeling my ass squish on his thighs" she thought to herself. Soon she noticed an irritating sensation - something poking at her. Pubic hair. She sat completely down and started dissolving the hair. He seemed more pleased than before? Curious.

She sat further down, letting her hot, liquid body spill onto his testicles. A moan. He's enjoying this. She enveloped his balls with herself, covering them completely and squeezing them gently. His mind was gone from the newfound raunchyness. She figured it out. And she knew what to do.

"You better hurry cumming darling, because this is your last chance to. I'm taking your balls as payment. You're getting castrated today."

His rational mind was completely gone. All that was present behind his young eyes was the desire to achieve his last orgasm. He started thrusting, she started bouncing. The caustic enzymes started eating away at his scrotum. There was something anesthetic in them, making it so he felt only mild pain. But he did feel his skin dissolve, and it was extatic.

"You really like it? Becoming less of a man? Your little balls aren't even that meaningful of a meal to me. But you deserve to lose them, no real man would crave losing his manhood. You're pathetic."

His balls were starting to dissolve, he felt them tingle, which ultimately made him release his load. Soon after, they were completely obliterated. He really was an eunuch from now on. He looked down to see them truly gone, and the wounds cauterized. What an outlandish feeling.

"You can no longer feed me cum. For shame."

"Feast on my penis, misstress."

"Your penis? I suppose you can't get hard anymore either way. That's a shame, I enjoyed the size...
Ah well, time to enjoy it one last time!"

He felt his dick dissolve while his exposed pleasure nerves were triggered directly, giving him an overwhelming orgasm, forcing him to scream with pleasure, as his penis disappears forever.

"Seems like I have no use for you anymore. You better scram, because you're delicious." She winked in a way that somehow was both innocently playful and thoroughly sinister. Naked, he ran for his life, and only laughter followed.

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Made this account for weird fetish stories, and this is my first one. Enjoy!

Edit: fixed (hehe) the formatting, hopefully