Aiden Smith walked into the locker room behind his new coach. He had just moved into town and had transferred to his new school's swim team as well. He was a little disappointed that he wasn't captain anymore; he'd have to wait until next year to be elected by his new teammates. He wasn't too upset, though, because this school had a much nicer program. He was getting an early tour of the athletic facilities before his first day of classes.
"This locker room was completely overhauled a couple years ago. Everything in here is under three years old. We moved from an open-area shower to individual stalls and the lockers actually lock now. Oh, come on!" he suddenly snaps when he sees a locker in the last row beaten up and bent out of shape. "Sorry, Aiden, I have to call the principal about this. Feel free to look around before class and our first practice is next Monday."
The coach leaves Aiden to finish the tour himself. He decides to check out the broken locker to see if anything had been stolen or if the locker was still strong enough to keep it's contents safe. Obviously not, because when he got to the locker and pulled on the handle it swung open easily.
Inside was a glob of black goop, which Aiden found both disgusting and curious. It wasn't very nasty at all, its surface was smooth and shiny. He curiously reached out a finger and hesitantly touched it. The goo suddenly shook as though it were alive and hooked tendrils shot out to latch onto Aiden's hand.
He yelled out in shock and shook his hand, but the goo was stuck fast. It quickly oozed its way up his arm and he could feel it being absorbed into his skin. He was too scared to fight it and watched in amazement as it crawled up his arm to his face and thrust itself into his mouth, slithering down his throat and up into his nostrils. His vision blacked out as it went up to his eyes and then back to his brain. He could feel it bonding with him and assimilating itself into every part of his body. He regained his sight and saw his body had grown to six and a half feet with bulging muscles everywhere, ripping through all of his clothes and leaving his naked, ripped form laying on the locker room floor. He ran to the bathroom to look in the mirror and saw a bodybuilder staring back.
"Do you like it?" a voice echoed in his mind.
"What did you do to me?!" Aiden yelled.
"Shh, you don't have to scream, just think what you want me to hear."
"What are you? What's going on?"
"Oh, sorry, that was a little rude of me."
"A little rude?!"
"Yes, but I'm afraid it was necessary. You see, I come from another planet, but my species is adapted to living in symbiosis with other creatures: we don't fare very well on our own."
"You're an alien?"
"Indeed, an alien parasite as you humans would say, but I don't intend to harm you in any way. On the contrary, I have made your body in peak physical condition. You see, my kind thrives on life force energy, meaning the more powerful our host the healthier we are. And the healthier we are, the more we can improve our hosts. It's a mutually beneficial and increasingly profitable relationship. So, I ask again, do you like it?"
"Well, it's a little too bulky. I'm a swimmer, so I need to be more streamlined and less V-shaped."
"I see, no problem."
Aiden's body immediately changed to that of the perfect swimmer. He spent some time flexing in the mirror and admiring his new form.
"What can you do about my lack of clothing, seeing as you tore mine to shreds?"
"Sorry about that," the alien apologized.
Black goo oozed out of Aiden's pores and transformed into a pair of black jeans and a black T-shirt, both tight to show off his muscles.
"Wow. I guess this is pretty cool. What all can you do?"
"Pretty much anything you can imagine. As long as it's touching you, I can change it. And since I want you to be healthy and happy for my own sake, I'll do anything you want."
"Awesome! Oh, crap! Class starts in a couple minutes, better get going."