Disclaimer: I absolutely do not own To Aru Majutsu no Index. The series is created by Kamachi Kazuma-sensei.

Hello! Hello! Welcome to my second fic! In relation to my first one, I guess you call this a side story/alternate universe/rewrite. Many of the characters who will appear here will be from A Certain Unscientific Paradigm, but with a slightly different twist, some might even have a completely different appearance, and some might turn completely evil. Paradigm will still be updated though so no worries!

Also, this fic isn't only about time travelling. There's going to be action, slice-of-life, and a bit of romance. Since this is partly a side story, I plan to focus it a little bit more on the non-canon's and clear out some of the stuff I left out in the previous arcs I've written in Paradigm. Hopefully, I can get ITEM to be more active this time around. But before anything else, your feedback will be much appreciated!

To those who followed and faved my first work, thank you so much! And to those I have letdown, I apologize! A special thanks to MistaSilentKiller, Sargent Carsh, and Luxraye!

Now please read and enjoy!

World_Line_Alpha: Prologue

World's_Departure

A door opened with a tiny creak, but somehow, it echoed inside that room which was whiter than snow. Perhaps it was because the researchers wanted to keep it clean as much as possible in order to prevent any irregularities like dust particles during their experiments.

And because of that, a girl named Tsuyuri Aki went passed that door with moisture all over her body and high school uniform. The cleaning agent machine was very thorough in her cleansing. Although she wished that wasn't the case because putting her necktie, blazer, knee-socks and the rest of her uniform back was such a troublesome errand. But the timid girl did not complain as usual. As an esper and a student of Academy City, she had no choice but to comply with the researchers' requests.

Her small leather shoes made small tapping sounds as she walked on the pure white floor towards the center of the room where a large man sat beside a large machine. The man occasionally flipped through the pages of the clipboard he was holding, in stark fascination.

This scene was playing out in front of her eyes yet again. She had already lost count how many times she did this routine, perhaps a hundred? No, that's not enough, maybe a billion? That sounds about right. Although the number of times it has repeated may seem unbelievable, those who work on the Attractor Field research team had already accepted this as if it were natural. "Time" here was a vague concept constantly being observed upon through scientific means. "Time" here did not simply mean the angles made by the hands of a businessman's wristwatch, but a transcendental fourth variable which exists in the entire universe in general.

Although right now, the newly turned freshman Tsuyuri Aki was not concerned with the entire universe or the vague concept of "Time". As any girl debuting in her first year, this was supposed to be a momentous occasion. She wanted to meet her new classmates and feel the atmosphere of being a high schooler for the first time, especially in such a nice weather such as this. Don't forget that those rowdy boys will be slamming their bodies with one another and making subtle touches with their bare skin—

"A-ahem…" She let out a small cough before she sat on the chair opposite the man, but he didn't seem to notice.

She could have been enjoying her first day of school, but instead she was called only to get cooped up inside this blindingly white research laboratory with her power developer. She sighed.

The man strokes his short beard. A name tag with "Tamaki Ebisuno" written in bold letters was hanging on his white lab coat. He would have looked like an esteemed researcher if not for the orange T-shirt under his coat and covering his big belly. If a third party were to look at those two, they would feel uneasy leaving a young, frail-looking girl alone in the same room as this man.

"Good morning, Tsuyuri-kun…" He said in a low grumble.

Tsuyuri responded by looking up from behind the fringes of her dark hair and nodding.

"I apologize for calling you out here all of a sudden. We needed to present some data at the upcoming conference so we were pressed for time."

"It's no problem, sensei…" She replied almost automatically.

"Now then, I know you have studied this many times before through the curriculum we have given you in order for you to understand what our research team is doing, but I'll have to ask you some questions as a refresher, understood?"

The girl nodded.

"Good." The researcher wrote something on the clipboard with his pen. "First off, what is the Many-World's Theory?"

Tsuyuri gathered her thoughts for a while before replying. "It is a theory which states that there are many and different kinds of universes parallel to our own… It is based on the principle that elementary particles such as an electron can behave both as a wave and particle at the same time…." She spoke about it briefly and recalled the image she invented for reminding her what the theory was all about, a long barcode with the black lines represented as electrons in their wave form while the blank spaces as electrons in particle form, and with each barcode labeled on each world. And the number of combinations those black lines and white spaces could take on that barcode was the number of possible worlds which could exist, possibly infinite.

But what is this so-called "world"?

In the past, Tsuyuri Aki had thought this only meant this round, blue and green planet she lived in, but now, to the recently turned freshman girl who became one of Academy City's Level 3 espers, it was everything, from the sun to the stars and to everything else floating about in space a million light-years away, everything.

And this world she was currently present in had an existing duplicate with a completely different barcode attached, and a subtly different kind of appearance. Perhaps in the other world she was attending the first day of school just as she wanted. Or perhaps in the other world that certain part was slightly bigger than what was with her right now.

She looked down on her uniform and sighed, still underdeveloped as ever.

In any case, those worlds which were like different copies of each other had come about when every single electron in the universe decided they would become a particle or a wave this time around. Although "decided" was not entirely correct. The actual process occurs when the that particle is observed upon and measured by a scientist. That is when the world splits into two, one having the electron behavior as a wave and the other as a particle. Each outcome presented a world and with each world created another outcome, making the number of worlds seemingly infinite.

That tiny observation created that change.

And this is where the underlying principle behind the well known abilities of the students in the city of the most advanced technology lies.

A scientist can observe that particle, but he may not be able to choose what outcome will be reached.

But the same cannot be said for the famous students of Academy City. Yes, there are students who have the power to control and manipulate the outcome each time. These people are known as espers.

"That's correct. And that's where your Déjà vu comes in, Tsuyuri-kun." The researcher known as Professor Tamaki remarked as his gray, monotonous eyes looked up from the clipboard. "Currently, time and space are some of the most elusive concepts science has not been able to fully comprehend… yet. In the entire world, not a single person has been able to fully grasp what these dimensions hold for our universe, not even me…" The man looked downcast for a second and brought his eyes back up with a small glimmer. "But you are here now, Tsuyuri-kun. Thanks to Academy City, an esper has been produced with the ability of observing different periods of time and space. Since you are the only one able to observe these parallel worlds, we have to record data on you as much as we can while the AIM diffusion field is at work during a Déjà vu."

Tsuyuri nodded, trying to look as serious as she could.

"Now then, please take off the Inhibitor around your neck. This space was built using the technology made to create the Inhibitor which prevents your AIM from making contact with other AIM's so we are free of outside interference. The possibility of a 'Checkpoint' interfering with the experiment is zero."

She did as she was told and put the black choker with a small rectangular device attached to it on a nearby container.

And when the researcher confirmed she did so, he pushed a button on the large machine beside his office chair, and the steel-covered machine which looked like a capsule opened up like a cocoon and laid out a narrow bed.

"Please proceed with the usual steps in preparation for a Déjà vu." The researcher gestured to the bed.

The girl breathed in and walked towards the bed before lying down.

Professor Tamaki turned to face her and tapped on the computer attached to the machine. "Brain waves all stable. AIM diffusion field stable. Heart rate, vital organs and all other conditions are all stable. RNG number assigned to this world: 567510. Are you ready, Tsuyuri-kun?"

"Yes, sensei…" The timid Tsuyuri Aki rested her head on the soft bed and closed her eyes. "I'll do my best." Before doing so, she gave one last look at this world she was about to leave, the clean white walls, that annoying orange T-shirt, the green apple lying on a desk next to a family portrait at the far corner of the room, and the door which led to her high school debut.

Her eyes switched back to the family portrait. She had not taken notice of it before, or it had never been there before, but it seemed out of place in this pure white room, including that apple. She couldn't make out who was on the picture, but there looked to be three people in it: a father, a mother and a child. It must have been a happy family portrait.

"Are you fully prepared, Tsuyuri-kun? When you wake up, you will be in a completely different world, although it may look just like this one. Your homeroom teacher may be different, the dorm you live in might be relocated, and you're roommate might become the person you hate the most. Are you prepared to accept these changes?"

"Well…" Tsuyuri opened her eyes slightly. There is nothing in this world I'm particularly attached to. Everything here is only temporary and will eventually vanish with a small poof. Although she hoped she got to see what the first day of school was like here. "Yes, I'm prepared to leave."

The man nodded. "Then I shall apply forced anesthesia to begin the Déjà vu sequence. Your mind will feel a little bit hazy."

If a third-party were to hear this, then they will definitely be concerned for the young girl.

But regardless, she nodded and accepted what she was given.

"I wish you a safe journey… for the both of us…"