Eternal has been bugging me to crosspost this here, and since I'm getting close to finish editing the second and third chapter I've complied. Be warned, this is a JJK crossover.
In 2007 stories of spiriting away have been passed down around an isolated Japanese village. In that village, two girls have been wrongfully identified as the culprits behind the recent uptick in disappearances.
This is their story. (Cirno and Dai take the place of the Hasaba sisters)

August, 2007

"Cirno." Daiyousei muttered, hugging her sister closer to her.

Cirno and Daiyousei Hibana huddled close within their stone cell with its iron bars, their blue and green hair intermixing. They had broken through the wood one on their first day, but the guard outside had caught them. It just made everyone else angrier and Daiyousei hadn't been able to fight back when Cirno was out cold. There had been disappearances happening since either of them could remember, people who were called uncles, aunts, and grandparents despite only having a vague relation to the community. Their mama, who Daiyousei couldn't remember the face of. She didn't know if their mama's disappearance was why everyone hated them, she didn't know what they had done wrong. They'd never made anyone disappear like mama had! They didn't do it, someone else was taking people! It made her tear up just thinking about How could they be responsible? Just because Cirno knew what 'Jujutsu Sorcery' was, didn't mean she did anything wrong. Cirno was her big sister, and a part of Daiyousei believed that if they just treated her nicely then they could all get along.

"It's okay, Dai, just follow my lead. You remember what I taught you?"

She nodded, muttering under her breath as she shook. "Take a deep breath, feel the cursed energy, take it into your gut, breathe out, feel it move through you, wrap your body in a shell of cursed energy, circulate it through your brain, and activate your technique."

She nodded, following her elder twin sister's command, remembering the days when they had first started to see things. Vague images in between the trees, a fluttering of wings, tiny things in the corners of their eyes. Cirno had always been the braver one, but back then is when her hair turned blue and her eyes had truly lit up with something Daiyousei couldn't name. Dai's own hair had turned green at the time. They were orphans, with only each other and the community to support them. Their mama had gone missing just like all the other people who weren't here anymore.

Cirno hugged her tighter. "Good. Just like I am."

A man from outside cut in. "Hey, did you–" Two people were outside the door, Daiyousei and Cirno had been tracking them by their breathing, straining their ears to hear over their own quick breaths.

"Of course I heard, I'm the one guarding them." The man seemed to laugh. "You're free to go inside and take a look, but don't blame me if they get you with their strange powers. The blue one iced over the cell and I don't want to see what the green one can do."

Daiyousei nodded. Cirno had called her cursed Technique 'Perfect Freeze' and it allowed her to make things cold. Cold, the room was so cold that Daiyousei could see their breath in the air despite it being August, see fire-fly like sparkles and snowflakes in the air, so cold that every inch of the room was covered in a thin sheet of ice. It was so cold but Cirno said it was the only way to escape. Daiyousei rubbed her head against Cirno, wiping her tears on her sister's tattered rags. "I'm scared."

Cirno rubbed her head against Daiyousei's. "Good. That way you'll have more cursed energy and we can escape."

They could hear people approaching from outside. Daiyosei's ears prickled, all were wearing boots, two heavier than the third. Her mind went back to their captors: the mayor and the two lackeys she always brought with her. She had always hated them: trying to follow them when Cirno had first brought Daiyousei with her to the forest to teach her about cursed energy.

Teary eyed Daiyousei nodded. She felt so guilty, their last escape had failed because of her, if she had been able to activate her Cursed Technique Cirno wouldn't have gotten hurt. The image of Cirno chanting to herself as her wounds closed was still burned into her mind. She was feeling teary eyed, she didn't want to hurt people but Cirno had said it was the only way to escape now. Her breathing slowed, evening out. Cirno hadn't blamed her, she hadn't said anything mean about her ever in her entire life. She'd make sure they could escape. It was their only chance, they didn't know what she could do and she didn't know what they'd do to them if they stayed. She didn't want to know.

The woman's keys were jingling. She always struggled to find the right one, even after days of practice.

"I'm ready."

Cirno nodded and buried her head in the crook of Daiyousei's neck. Then, the door opened with a tortiously long creek as the woman peered inside, her one hateful eye staring through the crack. Daiyousei held her gaze, and swallowed the fear in the back of her throat.

The woman slammed the door open, shattering the ice with a thud. Daiyousei flinched, holding down her cursed energy, forcing herself to not use her cursed technique in a panic. The three stood there in the entrance, the bright light of the full moon turning into silhouettes as they entered, cracking the ice beneath their feet.

"Now–"

Daiyousei ignored the woman, focusing on the cell and the door beyond. She breathed in. Their cell was three meters long and two meters wide with a two centimeter gap between the cell bars. She breathed out, surrounding her and Cirno in a shell of cursed energy. The woman was still talking. The door was four meters away. One of the men grabbed it to slam it shut. She needed to move them five meters for them to have enough clearance to escape.

The man began to shut the door, and–

–Warm. Daiyousei was warm, the cold leaving her in an instant as she and Cirno appeared on the other side of the door. Cirno sprung into motion, a bat made out of ice appearing in her hand as the door slammed shut behind them. The guard barely had time to react as her bat slammed into his crotch and the door froze close behind them.

The man screamed but Daiyousei held strong, holding tight to Cirno as she looked down the street. On either side were dilapidated rural houses, a few villagers were milling around, turning to see what the commotion was about. At the end of the street there were the stone stairs that led out of the village.

Daiyousei teleported again. They were at the end of the street. Several villagers screamed, they were looking down the stairs. There was a forest below, a thin dirt road cutting through it, leading away from the village.

She teleported them again. They were at the base of the stairs now. Even if their legs were short Cirno had assured her they wouldn't be fast enough with the stairs and the head start they had on them.

A second later her legs buckled as exhaustion hit her. Cirno took it in stride, holding onto Daiyousei tightly as she pushed off the ground. She could hear voices behind them. Her vision was blurry with tears, everything hurt but at least she wasn't cold anymore. She pushed off the ground as well, one foot after another as hard and as fast as she could.

They ran, they were running. Daiyousei realized she was smiling, they were free!

Free and breathing heavily. Only when they slowed down and the voices behind them had quieted down, was she able to make out their surroundings.

They were in the forest, the dirt road disappeared into nothing behind them and into the horizon in front. The thick foliage above blocked out most of the moonlight, shrouding them in darkness. Daiyousei felt exhausted. She assured herself it was okay, she and Cirno had been in the dark for days now and if she squinted she could still see in front of them. At the very least she could make out the trees that surrounded them, standing tall, judging them.

"Cirno! Cirno!" She was laughing. "Cirno!" She hugged her sister, really hugged her. Cirno reciprocated, laughing. They laughed and laughed, dancing, tumbling until they fell over. Daiyousei grunted as she hit the ground but she didn't care. They rolled to the side, hitting the base of a tree softly.

Cirno pushed off the ground first, offering a hand to Daiyousei. "Come on, let's go!"

Daiyousei took it, exclaiming as Cirno pulled her to her feet and let go, almost falling over again but righting herself. Cirno began trotting ahead as Daiyousei took a moment to wipe the dirt off her tattered dress, then she ran after her sister. When she caught up, breathlessly she asked: "Cirno, how long is the road?"

"A kilometer."

She tilted her head, feeling worry over her exhaustion. "How long is that?"

"A thousand meters."

Daiyosei froze. That was–she hesitated looking towards her fingers to count–like two hundred and fifty prions cells. She felt her heart drop. "Okay."

Cirno turned around, beckoning her to follow. "Don't be sad, it's only a couple minutes."

Daiyousei nodded and trotted after her again. Both girls soon slowed to a walk. She wasn't good with time, but she hoped that the villagers were still far behind. Her bare feet were starting to hurt. She was so cold in the prison cell she hadn't noticed it, but walking was really hard without shoes. The ground was uneven and rocky.

"Cirno, I'm tired. My feet hurt."

"That's okay, use your cursed energy like I am. See." Cirno turned around and raised a foot before dropping it back down. "I'm reinforcing my feet with it so I can walk without shoes."

Daiyousei nodded, taking a moment to look down at her own feet and closed her eyes as she focused. She tried to imagine it in her head, Cursed energy wrapping around her feet, winding like yarn into a pair of socks like the old women of the village knitted. When she opened her eyes, her feet felt less sore, and the ground beneath them softer.

"You can do the same thing with all your muscles, reinforcement is the most basic form of cursed energy manipulation."

Daiyousei nodded, even if the fuzziness in her head kept her from fully understanding what her older sister was saying. She looked side to side, the forest was dark and they'd get to the road soon, right? "Cirno?"

"Yes?"

"Where are we going?"

"To the road."

"After that?"

Cirno turned around and held a finger to her mouth, shushing her. "I'll tell you, but you can't tell anyone, okay?"

Daiyousei nodded. "Okay."

Cirno raised a hand, pointing towards the heavens "We're looking for Heida. Don't tell anyone, it's a secret," She seemed to realize something else then, "and don't tell anyone else about cursed energy or that we're Jujutsu Sorcerers, right?"

Daiyousei nodded.

Cirno practically hopped, smiling wide and making Daiyousei's heart warm. "Okay, because after this I have to teach you reverse cursed technique. That's how you turn cursed energy into positive energy, it's how I healed myself."

She tried to fight back the image of Cirno's injuries from their first escape attempt. Once again she didn't know what Cirno meant. She reassured herself with the knowledge that her big sister always knew what to do even if no one else did. She was always so brave and smart, and she figured everything out on her own, and planned their escape. Daiyousei's breath slowed, and her heart calmed, the beating in her ear trailing off to make way for the pitter-patter for her and Cirno's feet against the ground. Daiyosuei's ears strained and she frowned, when she was in the village she could hear the chirping of insects or the hoot of owls, but right now she couldn't hear anything.

Then, as a distant light shone in between the trees, a voice cut through the silence: "Hello?"

Cirno and Daiyousei froze. "Hello, is anyone there?"

Daiyousei sharply took a breath, just in time for Cirno to grab her and pull her beside a tree. Daiyousei swallowed her fear, feeling her heart rate accelerate again. All at once the light in the distance disappeared, blotted out along with all the moonlight by a wave of darkness.

"I know you're there." It was a girl's voice, sounding around the same age as both the sisters, but flat, slightly kind, and with an odd inhuman quality Daiyousei couldn't name.

Cirno put one hand against Daiyousei's chest, holding her against the tree as she gathered cursed energy in her free hand, summoning motes of ice.

"Come out. I don't bite." They could hear something flapping gently in the wind. "I have a lot of friends, I'm sure they'll be happy to meet you too."

Cirno tapped her fingers against Daiyousei, then raised them, readying a count down. Despite the darkness the sisters could keenly feel the other presence, casually floating down the path, her cursed energy a low scream as it suffused through the environment, growing denser the closer to her it was. Cirno turned her head around the corner, peering at the girl who answered her with a quiet sing-song:

"There you are."

Cirno clamped all her fingers down on Daiyousei and–

They appeared at the other side of the path as the girl–short, floating, blonde–lurch towards the space where they had been mere moments ago, her mouth enlarging for just a moment as she bit into the thin air.

Daiyousei's feet gave out from exhaustion, the strain from using her Cursed Technique hitting her. Cirno moved, a bat made out of ice exploding into her hands as she made a double handed swing at the monster.

The blonde girl turned swiping at Cirno but failing to hit her as the bat slammed into her side, sending her into the tree with a thud as the bat shattered into a hundred little pieces of ice. The blonde girl yowled, kicking off of the tree a beat later before Cirno's bat could re-form.

Cirno gasped as she was slammed into the floor, kicking dust into the air as the blonde girl's talons dug into her.

Daiyousei forced herself to her feet, swinging her weak, thin arms at the blonde girl with little to no effect. The girl raised her face to smile, red eyes and pearly white teeth gleaming in the darkness. She opened her mouth, stretching it wide as Daiyousei stepped back and Cirno gathered more ice. Then–

A fist slammed into her face with a flash of black. The blonde youkai went flying, taking a chunk of Cirno with her as she skidded down the road, dirt and rocks sent flying as she formed a crater in the ground. All at once the artificial darkness disappeared, giving the two girls a clear view of their savior.

He was a tall teenager, blonde haired and blue eyed, dressed in a pitch black uniform with a golden button: seeming like a goliath to the two girls as he raised his fist, the bandages around it smoking.

Nanami flipped open his phone as he slammed onto the speed dial for his driver. He brought the phone to his ear before the dial tone finished. "I need you back here stat–yes–I have two girls here, bleeding, emaciated, malnutrition, look to be seven or eight. They survived a youkai attack." He slammed his phone shut before the man could answer.

He stood at the intersection between the desolate earth road and the paved, lit, country road that shot through the mountains. He slammed his phone into his pocket, ignoring its buzzing as he reached down and picked up the bleeding blue haired girl. At her side the green haired one looked up at him with teary eyes. He nodded to her. "Everything is going to be okay now, do you understand?"

She nodded through sniffles. "Thank you mister."

He shook his head, his voice stern but caring. "Call me Nanami. You two are?"

"I'm Daiyousei, and she's Cirno."

"Good, help will be here right away. If any youkai come close, I'll exorcize them just like I did to that one back there." He gestured back to the crater where the body of the blonde-haired youkai was still dissolving into raw cursed energy.

She nodded, still trying to shrink in on herself. "Yes, Mister Nanami." She hesitated then, looking down at her feet.

"Do you have something to say?"

"Yes sir, Mister Nanami, it's just that we're nine, not eight."

He nodded, forcing himself to hold still and not run a hand through his hair in stress. He didn't want to make the girl think she was the source of his discomfort. He had the dubious honor of receiving the most multi-day assignments out of any second-year student at Jujutsu High, already being a Grade 1 Sorcerer at his age and having unwisely imposed a Binding Vow on himself titled: 'Overtime.' It restricted his cursed energy output during the hours of nine in the morning to five in the afternoon while he was on the job, in exchange for greater cursed energy for every hour worked over time. He bit back a sigh and looked at his watch, it was Ten O' Clock at night. He couldn't find it in himself to complain about all the long term assignments, it was his fault for making such a Binding Vow in the first place.

He just felt lucky he had gotten there in time to save the two girls. Either way, two children dressed in rags wasn't what he expected when investigating a series of rural disappearances.