AN: This is a three-part crossover, with Demon Slayer being the extra fandom. If you're not interested or familiar with it, please stop reading.
Springfield General Hospital, 11:50 p.m.
"Where am I?"
A woman woke up in a hospital bed. She noticed that the room was darker than usual, and there were no sterile IV bags near her or needles attached to any part of her skin.
Then she noticed her long pink fingernails, and orange tips at the ends of her long jet-black hair.
"Wait a minute..."
The woman jumped off the bed and saw a mirror next to it. She cautiously stepped in front of the mirror and saw a hospital gown, fangs, and light pink eyes—but those weren't her normal color.
"Am I...am I a demon again?"
She walked in front of her bed and bent down to see the name on the footboard.
Name: Nezuko Kamado
Age: 30
Sex: Female
Race: Human/Demon
Personalities: 2
Test Subject No.: 46
"Test Subject #46?" Nezuko squinted. It was hard to read with the limited light in the room. "And what do you mean by 'personalities'?"
Nezuko noticed green vines growing around her arms and legs. She tried to wipe them off, but when that was unsuccessful, she grabbed a pair of scissors and cut the vines off. They grew back almost instantly.
The door opened, two doctors in white coats entered, and Nezuko hastily jumped back into the bed, fast enough for them not to notice a thing.
"Okay. This is test subject #46, whose corpse we found in a Japanese cemetery," the male doctor said, while the female was writing in a clipboard.
"Doc, this is insane." The female doctor looked up from her paper. "You dug this body out of a Japanese cemetery? I knew Project Moonlight was a bad idea from the start—"
"Shut up or I'll turn you into subject #73."
"Whatever." The female doctor resumed writing.
"What are you doing to me?" Nezuko looked straight at the male doctor, who paced in front of her bed. "Aren't I supposed to be dead? You said you dug me out of a—"
"Okay, come with me, #46." The male doctor gestured toward the door. His female partner walked out of the room.
Nezuko reluctantly climbed down from the bed and followed the man. Only now did she notice she was barefoot.
Once she opened the door, her jaw dropped.
She was standing in an enormous chamber, with a beat-up copier machine in the center. Numerous other doctors in white coats were standing around, some nervously swaying side to side.
The only light in the room was from the moonlight shining through a large glass window right above the copier, which Nezuko approached to take a closer look.
It looked haphazardly repaired, with cracks and bent metal plates in some places, secured with duct tape. Signs were plastered on one side, saying "CAUTION", "WARNING", and "PELIGRO". Flies swarmed a corner that faced Nezuko.
"Okay, #46, would you mind lying down on the machine?" The male doctor opened the copier and coughed as thick black smoke came out of it. Eventually, it cleared, revealing a scanner. Nezuko hesitantly lay down on it as the female doctor cleared her throat and pressed a button.
A line of green light appear near Nezuko's feet, moving slowly towards her head. After it vanished, a large sheet of paper with Nezuko's backside printed on it came out the left side of the copier. Nezuko got off the copier and stared at the paper.
Then it began to move. The paper trembled as a life-size Nezuko clone rose up out of it—albeit with its eyes still closed.
"Jesus Christ," Nezuko muttered while examining her doppelgänger.
Every detail was copied perfectly—from the ribbon in her hair to every single toenail. Even the unusual vines were on it.
Then, out of nowhere, four men in hooded red robes came out of the dark corner of the room. They began chanting in Latin, and Nezuko and her double started to float. The men raised their hands, which began emitting jets of red light.
Suddenly, Nezuko felt light-headed. Pain formed in her stomach. She screamed, but red smoke came out of her mouth instead of noise.
Her pink fingernails were getting shorter, and she deduced that her pink eyes were turning back to normal.
Nezuko collapsed on the ground as the doppelgänger continued to levitate. The smoke entered its mouth, and its eyes flew open, with its pupils slits. The vines around its arms and legs turned red. It then fell on the cold concrete ground.
The clone woke up, hissed, and jumped on the already-dilapidated copier, before using its vines to grab onto the moon window and break it. Shards of glass fell all around the copier as the clone escaped the hospital.
"What in the world?" Nezuko ran out of the room and through the hallways, until she found a stairway. She climbed up and found herself on the ground floor of the Springfield General Hospital. She dashed out the door and barely saw the clone running towards a large rectangular gray building.
"Oh, great. More running. I thought this period of my life was over already." Nezuko sprinted after her doppelgänger, gradually speeding up enough to catch up with it.
The clone stuck out its tongue and climbed up the building.
"That's not very nice," Nezuko muttered as she forced her way through locked wooden doors. She saw another staircase, groaned, and ran all the way up.
On the way to the fifth floor, a robot popped up, blocking her way. "Halt! You need a special VIP pass from the boss—"
Nezuko pushed the robot aside. She could hear its malfunctioning voice and the clanking and clattering of metal, cogs, and gears as she climbed up.
After climbing up to the fifth floor, she saw the only door in the hallway—an ornate wooden door labeled "CRANDALL'S OFFICE". She barged her way through it, not noticing the card slot where the doorknob would be, and it fell off its hinges.
A tired Nezuko saw a bookshelf and a desk, behind which was a snoring woman wearing all-red clothing. Nezuko decided to sleep in front of the desk.
742 Evergreen Terrace, 2:45 p.m.
Marge was getting ready to go to the Springfield Meeting Center for her meeting with Crandall.
"Okay, Homer, I'm taking Maggie with me, so you'll be all alone in here." Marge hugged Homer tightly.
"Please tell me you'll be okay," Homer whimpered as he looked into Marge's eyes.
"I will." Marge kissed Homer's cheek, took Maggie, and entered her orange station wagon. "See you and the kids at 5:00!"
Marge drove off, the tires screeching against the pavement.
Just then, Homer heard the Simpsons theme coming from his pocket. He took out his MyPhone and saw that Bart was calling, so he grudgingly answered.
"Bart, didn't I tell you to call me only when you need to—"
"They've suspended school for today, Homer!" Bart's cheery voice said.
"Woo-hoo!" Homer ran to his pink sedan. "I'm coming to pick you up right now!"
Homer sped off excitedly.
Springfield Meeting Center, 2:56 p.m.
Marge came out of the parking lot, Maggie in her arms. They entered the building and Maggie sucked on her pacifier.
Aw, nuts, Maggie thought. Now I have to listen to a deaf lady shout at Mom for two hours.
Marge saw a staircase in the corner and climbed up.
However, when she almost got to the fifth floor, a beat-up robot popped up.
"Hal—hal—halt," the robot stuttered. "You nee—e—d a—need a s—special VIP pass from—pass from—pass from the bo—"
The robot's head fell down the stairs. The voice trailed off as what was left of the robot's neck ejected thousands of black cards. Marge picked one up and examined it.
It looked like a credit card, with "VIP" in large golden letters on one side and "PASS" on the other. Marge shrugged and noticed Samantha's office.
But the door was lying on the floor in front of Samantha's desk, barely touching a snoring woman in a hospital gown. Samantha, wearing red clothes, woke up and shrieked upon seeing the woman.
"Where are my hearing aids?" Marge heard Samantha mumble as she flailed around and frantically searched her desk. Once she found her hearing aids and put them in her ears, she noticed Marge.
"Ah. Marge Simpson." Samantha checked her watch. "Just in time for the discussion."
AN: I got the idea for the human copier from Gravity Falls. That machine will become pretty important when Marge needs it most.