To describe the idea of parallel worlds was to describe everything. Literally, as the acceptance of the idea of parallel worlds meant that everything was possible, just not in the same dimension. To many, it was enthralling to see how much could change with single, minuscule events. One atom out of place, and the world falls apart...

Truly, it was incredible, to be able to witness all these marvels. However, as with many of his alternates, or at least those who still existed independently of himself, Zelretch found himself bored of it all. Yes, he had seen many of the worlds, but he had never really intervened. Mostly because he could not be bothered to do so, and yet, he found himself longing for something. Something WORTH witnessing.

One would have to understand the innate curiosity that Zelretch possessed in order to even attain usage of the Second Magic. True, it was a magic beyond magic itself, but that was only part of his ability. It was his curiosity, his ability to look at a situation and question what if, that decided which Magic accepted him. This curiosity, strong as it was, brought him to search for something interesting.

That was how he found the small, seemingly innocent city of Fuyuki. Well, found would be an inaccurate term. He had been there before, helping to set up the silly Holy Grail War, and he had seen various parallel worlds of said wars. His favorite was definitely the fifth, with some of the more ridiculous versions of the fourth behind it. Part of his love for the fifth developed due to how much one man contributed to the differences between worlds. In one world, the man lived a happy life, living his dream until the end, falling in love with his servant. In another, the man learned how broken he truly was, saw the hell that his life would become if he pursued his dream, and went to do so anyway. In one of the darker versions of the war, the very same man cast aside his dream to save the woman he loved.

Yet each of them were truly fragmented. A better way to phrase it would be to say that they were all limited. The first was limited in terms of power, being the weakest amongst the three, yet the most skilled with a sword, having learned directly from King Arthur. The second was limited in terms of power, his magic circuits being weakened by disuse. He was also the most blatantly powerful in terms of magecraft, with absolute control over his reality marble by the end of the war. The final one was perhaps the most broken of all, essentially being a servant, a weaker one perhaps, but a servant nonetheless. The problem with the last one was that each time he used that power, his soul cracked, until it eventually gave out.

The differences between the three main worlds were so insignificant that Zelretch almost missed them, at first. The wrong word here, the wrong step there... In any other case, these slight differences would have resulted in almost nothing, yet whenever a World Difference encountered Shirou Emiya, the entire world changed.

Truly, if one wanted to see change incarnate, they need look no further than Shirou Emiya. Zelretch was bored, and Shirou Emiya proved interesting. Always overcoming the odds, even with his limits, just to fulfill simple goals...

Zelretch paused. There was that word again. Limit. Slowly, a grin began to form on his face, frightening the person he had been walking past. "Shirou Emiya... I have seen you at your weakest, overcoming the odds. Even with your limitations, you grew strong in a mere fortnight... I wonder what you would do without those same limits holding you down..."

Part of him believed the same things would happen, but another, much larger part, believed some things would change. After all, when dealing with someone that distorted, change was inevitable. With that thought, Zelretch knew where to begin.

It was only blind luck that got him this far, and even that was running out. As the world around him burned and withered, he could only be glad that he could only hear the screams, and not see the bodies. No, he was not blind. He was merely lucky enough to have walked towards a particular way which allowed for no visuals of the dying or dead. Part of him knew he should keep marching forward until he was safe, but another part, small as it was, yearned to help the ones crying out. After all, he had what others in this fire did not. Mobility.

Odd as it was, the boy was perceptive enough to notice people were slowing down before the fire, or even smoke, touched them, as if their very strength was getting sapped away by something. The boy did not understand what, or how, he only knew it was happening. Why it did not affect him was unknown. Perhaps it was and he had not noticed it, that blind luck having been more useful than he thought?

As he trudged on, he felt parts of himself falling away. Not physically, mind you, but mentally and spiritually. The first to go, oddly enough, was hatred. He did not understand it, hell, he did not even notice. What use was hatred to a boy of such an age?

Forward. Foward. Walking ever forward, the boy trembled. He could remember nothing now, not even his name. All he knew now was to walk forward, to escape this Hell. And yet, when he heard the sound of labored breathing, he paused. He turned, only to see a man trapped beneath some lumber. The lumber was placed in such a way that the man would be unable to escape and would die unless outside help arrived. For a single moment, the boy debated helping him.

To call what Kiritsugu's day had been bad would be an understatement equivalent to saying Enuma Elish was a light gust of wind. His lover died, his wife kidnapped, his wife dying, his greatest opponent in the war opposing him with multiple command seals, using them to counter his origin bullet, seeing into the Grail, experiencing All the World's Evil, getting cursed by said evil, losing his chance for his wish, betraying his servant once again, getting trapped under a piece of lumber on his way to try to save someone... no, today was hell. Quite literally, it was his own version of hell, being powerless and seeing all he loved taken from him. His family, his hopes, his dreams, one may claim his very soul was gone.

That was probably why he was not ashamed of being saved by a little boy moving the lumber off of him. True, the lumber was lightweight, but it was wedged under another piece, so that it was only movable from the top, which made Kiritsugu's position inescapable without help. If he had any pride left, if he ever had any to begin with, he might have cried at the fact that a boy less than a third his age had saved his life from a piece of fucking wood. Thankfully, he didnt.

"Thank you." He breathed outwards, feeling a strange sense of relief. Why would he be relieved at living further? With all his mistakes, all his failures? To live with them... was that not worse than death? Yet, his entire being rebelled at the thought of laying down and dying without doing anything. So, broken as he was, he stood up, taking the young boy's hand. Without another word, he began to guide the boy out of the fire. His research on the structure of Fuyuki helped him think of the shortest path out of Hell, odd as it was that he remembered it.

"There is nothing you can do?" Kiritsugu looked healthy, yet far more broken down than even directly after the fire. It had been a few weeks. Since then, he had adopted Shirou Emiya, named him, given him a home, and decided to get the boy checked out, to make sure the boy was fully healthy. The results were... not pretty.

As it turned out, because he had stayed so long inside the first, Shirou had inhaled more ash than was safe. This would normally have been solved rather easily, or killed him quickly, but because of the nature of the fire, it was different. Instead of asphyxiating like he should have, Shirou's lungs were cursed. To the doctors, it appeared as if he had the worst case of asthma possible. The fact that he had survived for so long without an inhaler was nothing short of amazing to them. To someone aware of the Moonlit world, like Kiritsugu, it was almost impossible to cure, even for specialized healers. It was not an overly powerful curse, unlike Kiritsugu's, it was a mild one at best, but the nature of it was corruptive and fed on magic to make itself even worse. That was probably why it had taken so long for Shirou to fully succumb to the curse. While Shirou had an astonishing twenty seven circuits, more than average, as well as an... odd crest, he never used magecraft.

Kiritsugu had revealed magecraft to Shirou immediately after adopting him, and Shirou had begged to learn. Kiritsugu was hesitant to do so, but promised Shirou that when Shirou was feeling better, he would teach him.

The doctor nodded solemnly. "Its not so simple to cure... whatever this is. His bronchial tubes are open and functioning, but his lungs are reacting like half the air he is breathing is smoke, rather than air. We put him on oxygen and it did not change. I have never seen a case like this. To be perfectly honest, the fact that he is alive even now is incredible."

Kiritsugu, his mind made up, nodded. Then he got to work. The only thing Shirou remembered of that day was a golden flash of light, as his father smiled at him. The Doctors and Nurses remembered nothing of either Shirou or Kiritsugu.

"So you want to be a hero, Shirou?" Kiritsugu looked towards the moon. It had always reminded him of his wife, and his daughter.

"Yeah! Of course! I want to be just like you!" Shirou looked... happy. And earnest. There were few ways to truly capture how a child looked towards their parent, when the relationship was filled with nothing but care for each other. They had, after all, saved each other's lives, even if Shirou did not remember what exactly Kiritsugu did.

Kiritsugu smiled. "Do you know what a hero is?" Shirou shook his head, knowing Kiritsugu would explain. "A hero strives to save everyone. Of course, saving everyone is impossible. Death is inevitable, after all, but... A real hero doesnt need to save their life, but to make their life worth living." Shirou did not know, but Kiritsugu was saying what he believed he should have done when he started upon his path. "A hero must strive to be the very best at everything he does, though he should not get angry when someone surpasses him. A hero will place the safety of another before himself, but... if you become a hero, Shirou, I want you to promise me to not forsake yourself or your friends. If you have to, in the moment where your loved ones are at stake... be selfish. Please, promise me." Kiritsugu knew better than to dissuade Shirou from his path, as he had inherited Kiritsugu's stubbornness.

Shirou frowned, attempting to look serious, but Kiritsugu thought he just looked adorable, trying to look so serious. "I promise." Hm. Even though he appeared adorable, he truly was being serious with that promise.

Kiritsugu's smile widened slightly, as his body relaxed. "That's good..."

Several years later, Kiritsugu passed away in happiness. Many mourned his death, including Shirou. On his grave, Shirou promised he would become the ideal hero that his father described.

Zelretch cackled happily. THIS! This was what he wanted! So much change by a few minor incidents, how extraordinary. "Now, Shirou Emiya, let us see how you do when the war comes into play!"

AN: No this will not be based on the movie Limitless, no matter how good that movie was.

So... how much changed? Quite a bit, Id say. Try to figure it all out for yourself if you want, but everything should become apparent next chapter. Hopefully, it will be longer than this one...