Peter Parker becomes black cat

You’d been trying to play it cool all morning, but the second the professor paired you with Mary Jane Watson your brain short circuited. She was already waiting by the bus doors when you got there, red hair pulled into a loose ponytail, the hem of her black hoodie just brushing the top of her jeans. She smiled when she saw you small, easy, the same smile she’d given you since you were kids and you almost tripped over your own feet climbing the steps.

“Partners, huh?” she said, sliding into the seat next to you like it was nothing. “Guess you’re stuck with me for the spider tour.”

“Could be worse,” you managed. Your voice cracked a little. She laughed, soft, and the sound settled somewhere low in your chest.

The lab was bigger than the pictures online. White corridors, glass walls, the low hum of ventilation that never quite stopped. Your group followed a bored grad student through the main facility while he talked about recombinant silk proteins and “non-lethal enhancement protocols.” Most of the class looked half-asleep. MJ kept leaning in to whisper jokes about the guy’s monotone, and every time her shoulder brushed yours you lost the next three sentences of the tour.

It happened when the group turned left at a junction and you both stopped to look at a side corridor the grad student had ignored. The door at the end was unmarked except for a faded yellow biohazard sticker that had been half-peeled off. MJ raised an eyebrow. You should have kept walking. Instead you pushed the door open because she was already moving toward it, and the two of you slipped inside before the rest of the class disappeared around the corner.

The room was wrong. Smaller than the others. No equipment benches, no computers. Just smooth metal walls and a grid of circular vents set into the ceiling and the upper half of every wall. The air smelled faintly sweet, like ozone and something chemical underneath. The door clicked shut behind you on its own. No handle on the inside.

“Okay,” MJ said, voice lower now. “That’s not normal.”

You tried the door. Locked. Your phone had no signal. When you turned back around she was standing in the center of the room, head tilted, watching the vents. A thin white mist had started to drift from the ones near the floor. It moved slow, heavier than regular fog, curling around her boots and then rising.

“Peter.” Her hand found your wrist. “We should ”

The mist thickened. You both started coughing at the same time. It tasted metallic on the back of your tongue, then sharp, then almost sweet again. Your eyes watered. MJ’s grip on your wrist tightened hard enough to hurt. The fog reached your knees, then your waist. You tried to pull your shirt over your mouth but your arms felt heavy, like the air itself had weight.

Something hot sparked under your skin. Not pain, exactly. More like every nerve ending had been switched on at once. You looked down and saw the veins in your forearm standing out, darker than they should have been. MJ made a small, choked sound beside you. Her free hand had gone to her own chest. The hoodie looked tighter across her shoulders than it had a minute ago. She swayed. You caught her, and the second your palms hit her back you felt it heat rolling off her in waves, her pulse racing under your fingers, matching the frantic beat in your own throat.

The fog reached your faces. You both dropped to your knees at the same time, still holding onto each other. The metal floor was cold through your jeans. MJ’s forehead pressed against your shoulder. Her breath came in short, shaky bursts against your neck. You could feel her shaking. Or maybe you were the one shaking. The heat under your skin kept climbing. Your muscles twitched without permission. Something in your spine pulled tight, then released, then pulled again. Your hands looked wrong—fingers longer, the tendons standing out sharp under the skin.

MJ lifted her head. Her eyes were wide, pupils blown. A thin sheen of sweat had started at her hairline. When she spoke her voice was hoarse.

“Peter… something’s wrong. I can feel it. In my blood. It’s ”

She cut off with a gasp. Her back arched hard against your arm. The fabric of her hoodie stretched across her chest as her ribs expanded, then contracted. You felt the same thing hit you a second later a deep, rolling pulse that started in your core and radiated outward. Your heart slammed once, twice, then settled into a new rhythm that felt too strong, too fast. The fog was thinning, sinking back toward the vents, but the heat wasn’t going anywhere. It lived under your skin now. Under hers.

You looked at your hands again. The skin along your wrists had gone pale, almost translucent for a second, then flushed dark. Fine, dark lines traced the insides of your forearms veins, or something that looked like them, pulsing in time with the new heartbeat. MJ’s fingers dug into your sleeve. Her nails had lengthened just enough that you felt the points through the fabric. She was staring at her own hand like she didn’t recognize it.

The vents had gone quiet. The room was clear again except for the two of you on the floor, breathing hard, still touching. Your clothes felt too small. Hers did too. Every small shift made the fabric pull in places it hadn’t before. MJ’s thigh pressed against yours and the contact sent a sharp, electric jolt straight up your spine. She felt it too. You saw it in the way her breath caught, the way her fingers tightened.

“Don’t move,” she whispered. Her voice was lower than it had been. Rougher. “Just… don’t move yet. I think it’s still happening.”

You stayed exactly where you were, her weight against your side, both of you listening to the new, too-loud sound of your own hearts while the changes kept moving under your skin.