18 years after the death of Himmel the Hero, in the Great Sanft Forest, located in the northern lands
Sukuna slumped against his house's exterior, amongst a dirt patch his mom had started calling his "training grounds" due to how often he had been out here.
It had been almost a year after the old man Rauch had given him a grimoire to study, containing within it a spell to braid dried grass.
The book had been read within two days. Memorized in a week.
There were many things he had to infer from the text. Despite being a beginner spell, it was written from the point of view of someone who had been a mage for a long time.
The fundamentals were often forgotten by masters of their craft. Sukuna had no ground floor upon which to build this spell. So he had to deduce how to do it.
Against his presumptions, mana did not work like cursed energy. It wouldn't reinforce, and due to lacking any form of polarity, it couldn't be reversed using anything like the reverse cursed technique. It was a stagnant, albeit potent, force that existed within himself, originating from his chest rather than his gut.
He had found that the easiest way to make a spell work was to believe it would, and visualize its effects and outcome. The book helped reinforce this.
He would believe that his mana could take hold of the dried grass, taken from one of the neighbor's barns, and could braid it. He could imagine how it would fold in on itself, curling into a basic braid.
A month was all it took for him to make a simple braid. A week after that, he could almost fully recreate the ornamental knots of the Heian era. The grass would braid itself, but wouldn't tie itself, oddly enough.
Perhaps this was the nature of all spells, as specialized functions of mana.
The rest of this time had been spent attempting to deduce the logic behind Rauch's 'Sculpted Smoke' spell. Months of starting a small fire, and pouring his focus towards the smoke. It was almost meditative. Sukuna felt the childish want to recite a prayer many times, looking at the smoke drift into the air.
The Buddha would not listen to him, and never had.
Sukuna went about making a small fire now, kindling piled up in a box-like structure in front of him. He had gotten the smaller sticks out in the field, now old enough to help reap the wheat they grew. The larger sticks he had to venture towards the edge of the forest in order to actually get some larger, proper, pieces.
The village was housed in a great forest, quite apparently, but it had only been a few months ago that Sukuna's dad had thought of beginning a lumber mill. He believed it would put their little village on the map, making it a proper town, or city if one were optimistic enough, which his dad seemed to be.
The fire kindled, and Sukuna leaned down to encourage the embers to burn with a breath of air. They glowed well in the shade of his home, and within minutes he had a fire.
He sat back and looked on as it grew, governed by the structure of the kindling. He focused above it, to the smoke it let off.
Without the book, it was much harder to not only visualize the effect, but believe it would work.
The memory of Rauch did, however. He remembered how he puffed at the pipe, and how the smoke curling from his open lips had shifted form as it left them.
He knew the spell was possible. He just had to think of how.
He had settled on a bubble. A bubble of water could catch smoke, so a bubble of mana could as well. He had his mana make a plane over the fire, the smoke catching and crawling this invisible surface even as he had it curl in from all sides, garnering shape to the smoke as it was enclosed.
From there, he had to shape it. He imagined the bubble elongating, becoming the bird's chest. Its head came next, then the feet. The wings were the last vague shape.
Then he focused on the details. The head was first, the beak and eyes to be exact. Next were the feet, sculpting the tiny nails. He painstakingly carved out the feathers in its form, each row of plumage adding volume to the shape.
It had taken him three months since he started using mana to recreate this spell from scratch, using his own logic for how mana operates. Those had been poor, blobby shaped smoke bubbles, lopsided and prone to failing at the slightest touch or movement.
With five months of work, he had been able to recreate it to the level Rauch had exhibited. Anatomically similar silhouettes, able to pass as shadow puppets.
With 9 months of work, Sukuna surpassed him. The bird resting on his finger looked like a cardinal that had fallen into a patch of ash and had never gotten cleaned of it. It was accurate to the feather, the movement, the way light cast upon it, every last detail and feature. One would not know this was anything but a bird unless they had the means of recognizing mana at a glance or ever had the opportunity to hold it, as despite the shape of it, it could only ever be as light as the smoke that comprised it.
The act of making it this precise had been a time sink priorly, nearly four minutes of concentration. With the familiarity granted him, Sukuna could now do it in under four seconds.
These nine months hadn't been spent focused on just this one thing, however. The base requirements for using magic lead Sukuna down the path of what Rauch had used to identify him as a potential mage in the first place.
That had been easier than he had expected. It seemed once someone cast a spell, they became sensitive to the presence and use of mana. Its very nature became a partial awareness for the user.
That's how he knew the boy his sister was meeting with for the last few weeks was dangerous.
He had happened upon them at first by accident, but the way his sister brushed her hair back and pushed her chest out to this teenage boy he had never seen before made it obvious that her puberty was taking control, making her act the fool.
The fact that the teenager had more mana than anyone else in the town was a separate issue.
Sukuna had been a curse upon the Heian era. A predator of a caliber that hadn't been seen since. A monster like him, even as changed as he tried to be, would recognize a fellow monster. This thing that looked like a teenage boy was one. The way it looked, it moved, it acted. All a clever facsimile of what a human could and would act like.
He never got too close to them as they flirted in the alleys of the village. He couldn't hear what they were saying, but his sister was certainly smitten, and the monster was good at manipulating her.
As such, she had been asking him to handle a few of her chores, so she could talk to him for longer. Sometimes he did, sometimes he didn't. Sometimes she left the chores undone anyway, and blamed him for not doing them.
He was willing to turn the other cheek, for all the good she had done in his life, but he wasn't going to let her be fooled by this thing.
He went to confront her yesterday, and he had finally heard them speaking.
"Are you sure?" Heben had said, curling a lock of pink hair around her finger. "It'll be so dark, I might not be able to find my way home if we meet up then."
"I'll bring a lantern then," He eased, hand sliding to her hip in a way that made Sukuna cringe. "It'll be the last time I can meet with you before I move on."
"O-okay," Heben stuttered, looking down at his hand. "The old well, after dark. I…" She trailed off, then took a deep breath. "I love you, Trügen."
"I know," Trügen said, leaning in close. "And I- oh."
Sukuna had made to interrupt before they kissed, but it seemed that Trügen was more perceptive than he had thought. The moment he had gotten within a few feet, he had noticed, turning his face to look at Sukuna.
"S-Senken?!" Heben cried, stepping away from Trügen. "I-It isn't what it looks like!"
Sukuna looked at her for a moment, then sighed.
"Mom wants us home. She wants you to help with dinner." He said, as if he hadn't heard what they had been talking about.
"Can't you do it? You love cooking with mom!" Heben responded.
"You left me your chores today without even asking." He countered. "Help mom or I tell."
Heben flushed, glaring at him, before she turned back to Trügen.
"S-Sorry," She apologized. " I gotta go. Tomorrow night?"
"Tomorrow night." Trügen confirmed, before turning to look at Senken again.
Sukuna frowned at him and turned, walking away. He heard Heben walk up behind him and felt her hand impact the back of his head in a slap, knocking his head forward.
"You are such a fucking brat!" She cursed at him, stomping off ahead of him with her longer legs.
Tonight, she was gonna go meet that scumbag in a private place, and who knows what would happen to her.
Sukuna let the spell go, and stomped the fire out, letting the smoke drift off and away into the sky. He set his sickle down on the ground, and walked inside.
He had to choose to walk this path. Inaction would do nothing but put Heben at risk.
He couldn't be the only one protected.