In case it wasn't clear by the title and description, this is a 'fanfic' (term used loosely) about Lucy getting it on with Mike in the form of a giant tarantula. If you still insist on reading it, I kindly ask you to pray for my sanity once you have finished.
The last thing Mike remembered before it happened was dropping a bottle.
The next moment he was a spider.
He had no idea how it happened. He had simply gone over to Lucy's house for the day, and the two had been looking around the basement for whatever interested them. They had brought several up and had spread them all over the kitchen table for later inspection. Lucy had just left to bring back one last thing from the basement, and Mike had been focusing on a bottle of some strange, red-colored liquid. The bottle was labeled, but clearly worn. As such, he could only make out a few letters: 's ex m chi'.
While he waited for Lucy to return, he pondered the bottle, wondering what it contained and why someone had labeled it in such a way. He had just gotten up from his seat to hold it up to the light, but a small slip caused it to fall onto the floor and shatter.
And that's when he became a spider.
At first he thought he had knocked his head hard on something and had passed out, but that was unfortunately not the case. For some reason he was a spider. Quite a large one at that. He also felt quite...lustful, but he'd figure out why he became a horny spider once he was somewhat accustomed to his new form.
Thus, he attempted to make sense of his new form. After a bit of experimentation, he found he could move somewhat well. It was weird as hell sensation, moving eight legs simultaneously. And that was just with the legs. Eight eyes, fangs, the huge abdomen...it was all a strange and horrible sensation, but eventually he was accustomed to his new form enough to move around adequately.
Now that he was somewhat accustomed to this form, Mike looked around with his new eyes, thinking of a way to put this sudden change to his advantage. While he was pondering this he heard a dreadful screech and turned to look to his left. Lucy stood in the doorway, frozen with fear. Her tail was puffed up to extremes and her mouth moved silently, possibly trying to make sense of what she was seeing. Mike's transformation had cost him the use of his mouth, but he would have smiled as a sick, but lovely thought crossed his little arachnid mind.
On the opposite side of the room, Lucy stood perfectly still. Here, in her kitchen, was a spider half the size of a cat, wearing a surprisingly sexy scarf. As sexy as it was, Lucy remembered that Mike had been in this same room moments earlier...could it be?
Lucy shook her head and screamed yet again. She immediately began to back out of the room, only to bump into her couch and fall back on it. The Mike-spider follow her out of the room, and suddenly the two were staring each other down. Lucy wanted desperately to look away from those eight emotionless, beady eyes, but something about them seemed strangely...inviting.
Again she snapped out of it. Lucy began to shove herself back into the couch, spreading her legs to put as much distance between her and what was probably her friend given a terrifying form. The tarantula slowly moved toward her, and she shut her eyes in in terror. This was it.
And then she felt something odd.
It took her mere milliseconds to realize what was happening. Her eyes snapped open and looked down. The spider's...head...was right between her legs. This was bad enough, but not as bad as the fact its fangs were pressed right up against her vagina. Her eyes opened wider than they ever had before, and all sorts of terrifying emotions crashed over her like a tidal wave as she realized the Mike-spider was sucking her off.
But Lucy couldn't help but gasp softly as the Mike in arachnid form continued to tickle her private parts with his fangs. The hair on the leg-sized mandibles caused pleasure Lucy had never felt before. It felt so wrong to have such a terrifying insect basically suck her off, but the amazing feeling the Mike-spider caused in her lower body was more than enough to make her forget the morals of such an act.
As the spider continued its routine, Lucy began to shudder with pleasure. She had no idea Mike was so good at oral sex, but here she was getting sucked off by her best friend in the form of a tarantula, and it felt amazing
Slowly, the intense sensation of the spider's fangs pushed her over the edge. She came hard, painting the arachnid's fangs with the result of her orgasm while she moaned. The Mike-spider slowly backed, away watching with all eight of its beady little eyes as Lucy's breath became erratic from the amazing feeling she just experienced.
Just a few feet from the couch, Mike observed his handiwork will all eight of his eyes. Like before, he was incapable of smiling, but would've done so if possible. Seeing Lucy spread out on the couch, panting from the 'work' he had done on her...it filled him with an odd sense of pride.
It was then that Mike was overcome by a truly terrible sensation. Whatever had happened to him seemed to be reverting, as evidenced by the horribly nauseating feeling of his excess appendages folding back into his body. By the time it was over he felt on the verge of throwing up, but a quick inspection revealed he was back to normal.
"...So it was you." Mike looked up as he heard Lucy's weak voice call to him. She was still on the couch, breathing heavily, but not as much as before.
"Heh, yeah, I guess," Mike chuckled nervously.
"Pffft, you're nervous jerk?" she asked, then shuddered soon after. "D-don't be...That was amazing..."
Mike smiled proudly. "My pleasure."
"Well, just let me savor this for a moment and we'll get back to what we were doing," Lucy told him, only to pause as she stared at him oddly.
"Oh, and you have cum on your mouth."
Disclaimer: I am not, in any way, into Arachnophilia. This started as a joke to see if I could write cat-spider sex, and it turns out I could. Then I kept going. I sure hope you got something out of this horrible attempt at a story, because I sure as hell did not.