Disclaimer: Death Note is not mine. The credit belongs to Tsugumi Ohba and Takeshi Obata. If it were mine, Light and L would be my pet cats, and it would be Cat Note.

Author's Note: There would be extras (OCs passing by for plot-related reasons, of course) in this story. The infamous notebook we've come to know will enter the narrative later. All in good time. For now, let's see how this Sayu is coping.

Prologue

She felt cold all over. Her eyes were brimming with tears as she looked up at the sky, as if begging anyone, please just anyone, to help.

And it came like a mercy. Like a dark fallen bird, she couldn't believe it.

She did not want anyone to stop existing. But it must be done. With a click of a retractable pen, they were written in.

And like popped bubbles, they just stopped being.

Look at the eyes of the girl.

She's not entirely lured into the game yet.

But the first domino had fallen.

Chapter 1: Parts

"Onii-chan!" a raven-haired girl in her pajamas knocked on her brother's room, "Why did you lock the door?!"

"Sorry, Sayu," her brother opened his bedroom and gave her a small smile, "Math troubles?"

Sayu wrinkled her nose momentarily. She knew Light, and she knew very well that such a smile was secretly smug, and if he wasn't too much of a gentleman, he would definitely smirk. He knew she would rather not ask help for her homework. But there were times when she really gets stuck.

She looked around his room suspiciously. Again his neat-freak brother, 'Light Border-line-OCD Yagami', as she had sometimes teased him, had everything in place and not even a smudge of dirt anywhere. Her room was not messy, but it would probably be in Light's standards.

They sat by his study table.

"Give that to me," Light snatched her book from her and contemplated the problems therein. Confusion dawned on his face to Sayu's satisfaction.

"Calculus?"

She knew that her brother had deduced several reasons in his big brain already, but she complied for conversation's sake.

"I'm taking a very advanced and special elective class in school," she raised her chin in a mock snob fashion. Light smacked her head gently with the book, and she burst into giggles.

"It's true! I told Mom not to tell you so I can gloat with satisfaction!" she added when her sibling raised his eyebrows.

Light laughed. "I know you're as smart as me, Sayu-chan."

Said Sayu inwardly rolled her eyes at the obvious joke, though she could not help feeling flattered nonetheless, since Light's intention to praise seemed present.

"Nevertheless," Light clicked his mechanical pencil in her direction, "remember that you owe me bento for my help!"

"No fair!" Sayu gave a frustrated laugh-cry, "I'm not cooking you packed lunch! This is an exception! I'm in Advanced Calculus! In Junior High!

She continued thoughtfully, "Well, Elementary Calculus really, since it's just an elective. But that's pretty advanced to take in Junior High. So there, Onii-chan!"

"Homework is still homework," Light sang, already slightly frowning at one item on the book he recognized as Sayu's mark as not-understood.

"And besides, I like your bonus bento-potato chips from scratch," said her obnoxious brother matter-o-factly, who then turned to explain the one calculus problem to her before she could make another sound from her open aghast mouth.

Sayu made sure to ask everything she did not understand in their current topic in Calculus and not just that one problem, since she was going to cook for the dang kid tomorrow for such service.

She would have asked about tips on the overall subject or advices for the next chapters, but her pride won't let her. She might have chosen very hard problems for Light under the guise that she had not solved them yet, but she knew that such plan would backfire and he would actually enjoy it. Hell, he might even figure her out and ask for another bento!

Sayu checked the contents of her schoolbag one more time, before collapsing onto her bed. Crossing her arms behind her head, she stared at the ceiling and let her mind wander.

It was hard to pinpoint when her sense of self as both her past self and Sayu solidified. She just knew that when she was younger, she had remained as her past self, only she was not aware.

Her child form did not care. When she was hungry, she asked for food. When she felt like drawing on the walls with crayons, she did it. She even remembered that yelling at her brother 'Why you Kirla!' while hitting him with a small doll on his forehead, was the closest thing she had ever come to confronting a mass murderer with his crimes.

Though she guessed that an annoyed nine year-old chibi Light did not count, unless you took the 'Once a murderer, always a murderer' in a whole new different step entirely. But her point remained; she'll never do such thing as to give herself away if she had been aware.

Which was in on itself good, or else she would have never learned to speak and write in Japanese easily if she quickly had her adult mind and not the young mind that was barely aware of its origins.

She had decided long before not to intervene. Original Sayu from the series, though she had suffered from the whole Kira debacle, had never actually died prematurely, and she would rather play it safe. She might be witty at times, smart even, but she did not hold a light to Light. Forgive the pun.

She was simply prepared to live this life until her probable next reincarnation. This said life is weirdly full of crime, like it was really made for Kira, the criminal-killer. She just had to look at where she was living right now! She did not remember the specific statistics, but Japan was supposed to be one of the countries with the lowest crime-rate. So much so that there's even a joke going around that people did not even lock their doors at night. She would not even be surprised if she learned that it was not a joke! But Japan in this certain anime-verse? Words failed her.

She let all of these thoughts go before closing her eyes in bed. But one thread caught before consciousness left her. It was her worry about her brother's locked door and the little black book it might entail.

It was beautiful. The sun was bright and was bathing the entire city with its warm glow, but it was also windy enough for anyone not to find the weather too hot. The birds seemed to agree; one can hear their tweet as they rounded over the trees near the school building. It was the sort of beautiful day you would think everything would fall to place.

This was what went through Sayu's mind, as she gave this suspiciously innocent facade a once over. It was not like she noticed a pattern of good weather equals bad day in this universe, but today she had a gut feeling. Or maybe it was missing the bus because her alarm clock broke and did not go off that made her biased. And she still had the nerve to cook Light's bento, though it was a small bento given the circumstances. Augh! Why didn't she let the guy starve?!

"Sayu, you're spacing out the window again," Megumi, one of her close friends sat across her at their usual lunch table.

She gave Megumi a large smile, "I'm waiting for something to fall from the sky."

"Funny," Takeshi, their friendly glasses-wearing nerd-ish chum, said and sat beside Megumi, his girlfriend.

His girlfriend gave him a peck on the cheek and he in turn pressed his forehead on hers momentarily.

"Eww! Get a room, guys!" Matsui gave them all a grin as he sat on the last available seat by Sayu.

She knew. Takeshi. Matsui. She did not know whether to laugh or cry at the coincidental choice of names regarding the Death Note franchise. Though she entirely blamed the laziness of whichever god placed her in this world.

Anyway, Sayu laughed and stared fondly at the couple. Their relationship was actually comforting to her because for an anime-world, it was the total opposite of what you'd usually see on anime. Megumi was beautiful and tan, while average but sweet and smart Takeshi practically went head over heels. That wasn't what made them un-anime-like, but the way they treated each other.

She's not saying that every anime couple was love-hate, and she has nothing against that except for the fact that maybe it could sometimes romanticize emotional and physical abuse. Sorry, but that was her opinion. But, anyway, love-hate was usually the trend she saw. And though they also had bad times, Megumi and Takeshi were also just so nice to each other most of the time since day one. And Sayu was always comforted by some things that could ground herself a bit back to reality no matter how subtle. 'Her' reality that was not Anime.

Everyone on the table went on to listen to Matsui rant about what he hated about the new substitute teacher on third period. Sayu was nibbling on her rice cake when they heard the commotion. She looked up the window once more.

It was the school bully outside on the school ground. He and his friends were surrounding a boy smaller than them on the school lawn. She recognized Haruhi from her English Grammar class. She looked on as Haruhi got punched. Everything was still the same when Sayu last stared out the window only moments ago, but now she saw rotten leaves of rotting trees. The tweet of the birds were absent but the rumbling of dark clouds were there.

Sayu shook her head, a confused expression on her face as she studied her dumpling next to her rice cake. When did she care?

Granted, her preference of a nice lunch did not include unnecessary violence, and she found Ken Saotome's bullying tasteless, but she should not be too shocked given the realities of this life.

"Weh!" Matsui exclaimed and she looked up at the fight once again just in time to see Haruhi punch Ken. Ken's friends retaliated by hitting Haruhi as well.

"That's the first time I saw Haruhi show some courage," Megumi said in a hushed disbelieving tone, as Takeshi put an arm around her.

It was true. Haruhi Shinohara was a quiet boy. He's also one of the usual targets of Ken when he wanted some money or if he simply wanted a punch bag. Usually, not complying with the first option would result to the second one.

Today, Sayu mused as she saw some teachers and staff appear to break off the fight, it seemed like that's exactly what happened. She saw Ken give Haruhi one last death glare before he and his gang got taken to the principal's office. The dunderheads, picking a fight on the school grounds, of course they would get into trouble.

"Yagami-san,"

Sayu's finger's twitched, irrationally aching for a Death Note when she heard him speak.

"Yes, Nonako-san?" She said coolly at one of Haruhi's tormentors along with Ken, whilst writing her history notes.

She sneaked a look to check whether their teacher is listening in. She returned to her notes and saw a rose lying on the open page.

"Nonako -"

"I know. I know. You're not ready for a relationship yet. Yet you hang out with that Matsui Miyako a lot," Nonako sneered.

"I've told you before that we're just friends," Sayu said frustratedly that she actually cut herself with a lone thorn on the rose's stem. She flinched.

"That's bullcrap! I see how he looks at you, Sayu!" the boy whispered fiercely.

She did not try to correct her into saying her last name instead. Whereas other suitors backed down when she told them that she would rather stay single for now, Hide Nonako was one stubborn piece of work. She reckons Nonako thought of her the same.

Nevertheless, credit's where credit's due.

"Giving me this rose is very sweet of you, though. Thank you."

Nonako was silent. Sulking perhaps. She knew that he did not want a thank you, but a yes.

"You're bleeding," he then said.

And before she could stop him, Nonako took her finger from the flower to put her wound in his mouth. Sayu squealed when her finger was half an inch away from his lips.

"Yagami! Nonako! Don't you dare think I can't hear you over there. Detention!"

Nonako smirked. Sayu groaned. Detention would not be detention for Nonako because she would be there.

"Sayu, you're having your things littered all over the living room again," her mother in an apron chastised her, though was also giving her a small knowing smile as she fluffed a coach's throw pillow.

"I'll clean it all up later, Mom. Promise."

After the bad morning start, the lunch time fight, and the grueling detention, she needed this, though she was thankful that strict Professor Nakamura put another three pupils in detention and never left them alone. She did not like the thought of being ever alone with Nonako-san.

Trying to lift her spirits up, after school, Sayu went by her favorite mechanic's store and bought some components she had been planning on buying. She had a blueprint in her bag and list of tools mixed with her school stuff of late, but she had not gotten around it.

And what was her mother talking about? Sure, it was a bit a lot, but all of the small gears and tools were arranged on the wide circular coffee table according to their function. Screwdrivers and wrenches of different sizes lay on one side, the circuit boards, wires, and body cases on the other. A closed manual book and a large open blueprint lay in front of her.

Though, Light would probably arrange everything more immaculately and not just bunched up together. Though if he did, there would not be any more room on the table. And he would not do that because he knew that the living room was only a temporary place to work at.

"I'm home," she heard a flat voice call out.

Sayu looked up from the blueprint, and caught her brother looking at the watch clock with those bored dull dead eyes he sometimes wore when he thought no one was looking. Then again, his long emo anime brown hair probably did the hiding half the time. Sayu from time to time wondered if Light really could not feel it when his bangs poke his eyes.

"Onii-chan!"she cheerfully waved a wrench at her sibling.

"Sayu! It's been a really long while!" exclaimed her Onii-chan, his face lighting up at the array on the coffee table.

She studied his tired but happy face. A facade? Was he reacting this way because it's expected of him? Or was it really genuine? Sayu shook her thoughts away. He would probably truly enjoy this halfway through tinkering on the gadgets.

If he seemed preoccupied, it could be the Death Note he could be thinking of and how this activity was taking his time away from his murder spree. But that was ridiculous, there had been no news of criminal heart attacks yet. Which also totally ruined her theory on Light's closed door last night. Besides, Light really liked his privacy sometimes anyway. And also, why would Kira not kill anyone right away?

Unless, he just found the Death Note this afternoon...but then what was with the zombie expression when he entered the house? But then again, that did not mean anything either because -

"Sayu."

"Hmm?"

The girl had been staring at the blueprint for quite a while, that she did not notice Light sit beside her on the floor and grab a screwdriver. He had been studying the said print over her shoulder.

"I think we should start with..." Light grabbed some circuit pads and pointed at one part of the blueprint.

She agreed. "I should think so too. I suppose I should start preparing some of the limbs while you do that."

Light nodded thoughtfully, already concentrating on the task at hand.

A certain silence of mutual camaraderie followed as the two siblings worked. Sometimes Sayu would flip pages of the manual and would inquire Light with one thing or another, on which he would reply something briefly. But aside from that, only the screechy sound of wrenches and screwdrivers would be heard.

Sayu looked over her work just to proudly see Light being devoted on the job. Project Make-Light-see-some-good-in-the-world was not a picnic, though it was something she had worked on when she was younger and had not made up her mind about whether or not to divert from canon. Now, the Make Light See Light Program, an anti-Kira non-government one-girl organization is now canceled, now that she decided she would not exactly intervene with the main storyline.

But back then she was devoted. She had even got other names thought up like Make Kira Nicer Agenda. Maybe Light would do an extra effort not to kill suspected criminals who might be innocent.

But she had to stop. Obviously, it means Raye Penber, the FBI agents, and Naomi Misoura would be spared if Light really didn't kill innocents. This would throw the said storyline into a whack.

But it was just back when they were both in grade school; Sayu decided that Pre-Kira Light was not so bad after all. Even though he already had an inflated ego even then, Light was part of her family. Maybe she was just biased but he seemed like a good kid in general when it came down to it. This was what caused her to launch the mission.

One of Light's probable root problems was thinking the world was so boring that it simply offered no challenge for him. Perhaps this was why he would later abhor it and see only the negative.

So she did this. She knew the early 2000s was not that advanced yet, but she had to try. And perhaps at this time in this dimension, what she was seeking was already available even if it was not in her own reality.

Thankfully, it seemed like such did exist here.

Using up all her savings from her allowance, she had asked brainy Takeshi who was already her classmate back then, for blueprints necessary in building a small robot and directions to where she can buy the stuff needed.

It was not easy sneaking off after school to buy this, when it was her father's strict orders to catch the school bus right after dismissal. She had to get a ride behind Takeshi's bicycle and quickly get off it before they realized that she did not come home from the mentioned bus.

She also had to make three trips before she got everything she needed. And even if Takeshi was by her side, her fear never left her. She was younger and more vulnerable, and she kept clutching the taser in her pocket every time a stranger on the street goes too near.

But the store owner happened to be really nice, Takeshi's older brother. They helped her and gave her good instructions. And one idle afternoon, she had gone to Light.

"Onii-chan!" she said, at that time waving a small light bulb at him.

"Sayu?" his brother also just got back into the house, was still in his school uniform, his light brown hair more cropped, and was thirteen years old. Meanwhile, she was ten.

She remembered that the tools and parts needed for making a robot was on the dining table that time. It was a hot afternoon and Light was probably on his way to the kitchen to get a glass of water when she had surprised him.

Light approached the table in a perfectly concealed awe Sayu almost did not see. The blueprint was simpler then, but she had noticed Light looking at it hungrily. Well, it was not obvious on his composed neutral face, but she could see his eyes betray him for a nanosecond there.

"Wanna help?" Sayu said in a sing-song voice.

Light gave a small grin at the challenge.

That night their parents ate on the sofa of the living room. Strict as Soichiro is, he was a softie to 10 year-old Sayu's wide teary eyed mumble of "Please, Daddy. Just this once?"

And besides he could not help but be fascinated when he saw his two children enthusiastically engage in something so intellectually inclined.

Of course, that was not to say that they just turned into genius engineers overnight. Well, maybe except for Light, but even then it took him a while to figure things out. But over the years, they became better. Sometimes, they worked solo, but most of the time they had worked together. But with Light's tennis matches and interest in his dad's detective career, their times like these slowly deteriorated. Sayu knew better though.

"Do you remember," the now 17 year-old Light started, still fiddling with some wires, but effectively startling her from her reverie. "When we won second place in that one robotics contest in Tokyo?"

"Yes, you kept telling me I screwed up because two of the legs would not move."

Sayu remembered the impressive robot. It was two feet tall and a foot wide, and it had eight legs. It was Light's own design.

You could see the wires and mechanical innards, but that actually made it more endearing when you knew it was made by some individuals who had not even reached legal age yet.

Even now, you would see it on the wall by the stair landing, a framed picture of the robot, with the two of them holding a trophy. Light was frowning and would not look at the camera.

"Can you blame me?" Light said, "You love to sabotage with whatever mech I'm currently working on. At first I thought I was doing something wrong. And then I found some thorn missing parts in your room."

"And do you still remember why I did what I did?" Sayu shook a tired hand, before grabbing a screwdriver and small wheel.

"Yes," Light stopped working, and his gaze looked far away. "I was expecting you'd say you were jealous. But you started spouting things like I was too perfect and that I needed to learn how to lose. That maladaptation is dangerous."

Sayu ceased what she was doing as well and looked at Light. "And why is it dangerous again?"

"Really, Sayu?"

Sayu shrugged. "Whatever. I was a crazy girl back then. But I don't remember every craziness."

She continued to refer to the blueprint and looked at the robot foot that she's trying to put wheels on. She cursed, when she realized that she had put it together the wrong way. She proceeded to take one wheel off with the screwdriver.

"And I did not sabotage the Tokyo contest by the way" she added as an afterthought.

"Sayu, you looked me in the eye, as serious as a cherubic girl at age twelve could be and told me that if everything I do I get right the first try, there will be a time that I'd get it wrong. And it might happen in a more serious situation. You said that I wouldn't be able to accept such failure, that I'd search for reasons that what I had done was right. Then I would do it over and over again because for me it had become the right thing."

Sayu faced her brother and smiled sadly. "Sounds like a jealous little girl to me. You have nothing to worry anymore, Light. I promised I would never sabotage anything for you again."

"Yet at the Tokyo contest, you were so suspiciously happy," Light scoffed.

She shook her head. "Because second place have always been enough for me. I didn't do anything sneaky because I didn't want to take any chances. I already said what I wanted you to know. If I did something to our brilliant robot, we might not even win any of the prizes. I could be ambitious as well to an extent, you know.

"And if I really had sabotaged the two legs of Primo Octopi, shouldn't you have been smart enough to spot it, Light my dear genius brother?"

Light laughed. "Alright, alright, Sayu. You've convinced me."

"Like I've been trying to convince you these past few years!" she called to Light who had stood up to go into the kitchen for snacks.

"It's not like I've been sulking and ignoring you or anything!" he replied.

"Yeah," Sayu huffed. "You just don't make robots with me anymore."

"Well, I do now," Light came back, handing her an open pack of chips.

Author's Note:

Sayu here doesn't actually 100% believe that the maladaptation was what really caused Light to be Kira. However, she was simply tackling one of the theories about the cause of Kira's existence.

Also, I got the theory on Tumblr. Forgot the writer, but I think the title is Hellscape. It's a sort of psyche profile analysis of Light. Very interesting. Thanks for the idea!