Mike was an average young man. He had found a misterios black thong lying by the door of his apartment. He picked it up, entered, and was surprise by how smooth it felt; he had never felt such silky fabric. He may try it on after having a shower and with that thought he tossed it onto the bed and went to the bathroom. A few minutes later he came back to his bedroom with a towel wrapped around his waist only to find that the black thong seemed to have moved. It was lying on the closest edge of the bed instead of the centre where he had left it. Maybe his visual memory was simply not as accurate as it used to be.
He took the towel from his waist and started to dry his hair when the black thong suddenly jumped to life. It started to crawl towards the naked guy. Mike saw it and jumped back out of sheer panic but before he could really react in any other way, the thong literally jumped onto him. It landed right on Mike's groin and in just a second it split creating three arms that wrapped themselves around Mike's waist and between his legs and arse cheeks fussing together over them. Suddenly and in a movement too fast to be processed, he was wearing the thong.
Mike threw his hands immediately to the black garment that now covered and perfectly hugged his package to try to remove it but shortly he discovered that he could not grab it, it was totally glued to his skin. He could not understand how that was even possible. It was alive? Maybe it was not just a thong. He didn't know what to think. The only sure thing was the fact that he was incapable of removing it.
At least, it seemed to be totally inert now, totally glued to him but nothing more, or so he thought. He didn't realise that the calm that he was feeling from this fact was the thong's first effect on him. He began to consider how good it felt, it perfectly fit hit and hug his package very nicely, it seemed to be custom-made for him.
Mike began to feel something inside his arse. The black fabric was somehow inside him and it seemed to be doing something. Mike realised that at least he should feel scarred but instead of that he began to be aroused; there was something terribly erotic about how this black thong was doing something to him.
His cock began to grow but the confines of the thong expanded with it remaining totally snug, tight like a black condom. Mike grip his erection through the black fabric and began to jack off. The feeling was incredible; he had never experienced anything like the overwhelming wave of arousal that invaded his brain when the black fabric began to stimulate his glans.
The thong was also expanding inside his arse and stimulating his prostate. Mike was entirely lost to the sexual bliss while the black thing began to implant deep in his mind the idea that finding this thong was the best thing that had ever happened to him. He would never again try to take it off. And that was when the symbiotic thong began his transformation.