Kyle ran to Jen's house as fast as he could. He sprinted at an Olympic pace, the curse giving him incredible stamina. He had no idea why he was running to her house, nor did he even know where it was. Pushed by an overwhelming urge, he ran for 10 miles through suburban neighborhoods and shopping centers, parks and backroads, industrial parks and even some farms, until he reached the other side of Glendale and Jen's house. He vaulted over the gated community's fence, never missing a step as he ran past McMansion after McMansion until instinct told him to stop.
He had no time to marvel at the mansion she lived in as he turned, panting, and opened the unlocked front door. Bounding up the steps two at a time, he turned to the left, and then, guided by the curse, through the second door to the right. Jen's bedroom. Opening it, he saw her, and she saw him. He wanted to scream, or vomit, or both at the same time.
What was laying on the bed was Jennifer, or at least, what remained of her. A teardrop-shaped blob took up most of her bed, her limbs weakly reaching out towards him. He could see her internal organs pulsing through her translucent carapace, her body clearly in the larval stage of something, but he had no idea what. The curse pushed him forward, closer to the disgusting mass. She mouthed something to him, and he understood immediately. Carry me on your back, she demanded silently.
Kyle obliged against his will, and walked towards her bed, turning around when he reached her. He wanted to scream as her strange, wet body gripped him for dear life. He stumbled forward as she pushed her mass onto his back, impossibly heavy. She must have weighed 200 lbs, far more than Kyle's twiggy body.
"What the fuck are you?" he asked, frightened. He never got a response, Jen was completely silent.
He realized she wasn't even breathing, her gills keeping her alive through the curse alone. It frightened him more feeling her face press against the back of his neck to know she was alive, while not feeling a single breath. His legs buckled under her weight, but never gave out. The curse gave him the strength to haul her cumbersome body down the stairs and out onto the lawn. As he fell onto her front lawn, he tried to get her off of his back, but she was stuck. "What ARE YOU?" he screamed. But then he went quiet as a tingle shot down his spine.
His changes came on in the blink of an eye. His feet burst through his shoes. He screamed in silent agony as his legs distended, chitinous skin extending over them. His jeans shredded as they grew larger and larger. He felt his ass push out impossibly far behind him. It hardened, covering itself in a bony exoskeleton. He felt Jen crawl on it as it grew, soon dwarfing his upper body. He wanted to cry. What the fuck is happening?! he thought. More legs grew in behind him as his newly chitinous feet began to reshape. His toes merged, his big toes extending out while the other four came together, becoming huge crab claws. His new legs splayed out underneath as his groin hardened over. He shuttered as his urethra pulled open, rearranging itself into alien new mouthparts. He completely forgot about Jen in the rush and horror of the moment, the flood of new sensations overwhelming his brain while he continued to expand.
As for Jen, however, she was on a mission. She suddenly found the energy to pull herself along Kyle's chitinous new rear, using its growth to her advantage as it pushed her along. His kneeling position left it pointing up into the air, perfect for her to gain access where she needed it. Guided by pure, horny, parasitic instinct, she crawled until she found what she felt was a suitable gap in his exoskeleton. She injected herself into his body, her head and nearly all sensation disappearing.
------------------------------------
Lost in the sea of panic, he wasn't sure how long he'd been growing, but his lower half had become truly leviathan. He felt meter upon meter of new flesh grow in underneath him, pushing him far higher than the houses, and expanding to a scale he could not possibly comprehend. Once it was finished, his new crab body was 540 meters wide, 450 meters long, and unbelievably heavy. His legs splayed out on each side, bringing his full width to over a kilometer. His new pincers were over 200 meters long by themselves, and were incredibly heavy and muscular. He gingerly brought one up to his human body and was shocked by the scale, unable to comprehend the city-block sized claws he now possessed. He felt minuscule attached to this gigantic body, until he looked around. The McMansions he was in awe of only hours before barely even registered anymore, his torso now resting 228 meters above the ground. They seemed almost toy-like to him. Kyle's crab body dominated the landscape around him, giving him a permanent skyscraper view. He was far taller than any of the buildings in town, and he wasn't even standing. He wanted to cry as he realized he would never be able to enter into his own house again, or talk face-to-face with normal people, or wear clothes. He didn't even fit inside cities anymore, let alone buildings. The distance to the ground suddenly felt impossibly large, when he realized he could still feel it underneath him.
As he sat in the ruins of Jen's old neighborhood, he felt a slight prick at the joint of his exoskeleton, but thought little of it. It was hard to differentiate it from the ruins settling underneath him, or the trees crushed under his legs, or the houses, the cars, the infrastructure buckling beneath his immense weight.
------------------------------------
While Kyle came to terms with the horrors of his new existence, Jen had been busy. She quickly moved through the next few stages of development, shedding her exoskeleton and establishing herself within her new host's flesh. The now minuscule 1.2 meter exoskeleton was crushed long ago during Kyle's growth; he didn't even feel it underneath all of the other rubble. Jen felt her body change again, organs disappearing and rearranging a second time, and then a third. In the blindness of her nearly organless form, she felt herself spread within him. Tens of meters of parasitic flesh extended through his body, soon becoming hundreds. Even in her dim awareness, she was shocked by how big he was, and could feel him still growing as her tendrils pushed deeper and deeper.
She felt neither thirst nor hunger as her tendrils spread. She felt nothing at all except for growth and pleasure. Her tendrils pushed and pulled, working their way around his organs and through his muscles. They grew in an impossibly complex maze, drawing nutrients from his oversized body to feed hers. Time seemed to stand still as she continued to infiltrate his flesh, some of her branches even reaching his human torso. They spread through his limbs and into his pincers, but she felt them especially dense around his organs, siphoning his energy for her own use. Days and nights passed for her like seconds. Her awareness was dull, dream-like, with hardly any sensory neurons to fire. She could vaguely feel him move, seemingly unaware of her presence, but even that felt impossibly distant. Suddenly, however, a bright flash of light blinded her...