I do not own Fate/Stay Night and stuffs:

o. o. o.

That night Kiritsugu and Shirou were once again in their shack which Shirou had chosen to be his workshop, the core of his research as a magus…

Kiritsugu was fairly certain that if any high ranking magus had actually seen the state and location of the boy's center of operations, filled with random mechanical rubbish and no magical appliances, they would either laugh their asses off and pass the whole thing off as some sort of joke…

Or more realistically, kill him, the boy, and then torch the place down in order to rectify the insult done to all of those who practiced thaumaturgy.

Still, the shack served its purpose. Once more, Shirou started off the night analyzing over a dozen random items inside, telling his father what he knew of the object and what was wrong if it didn't work, carefully going over each and every detail as he did so. Since Shirou actually knew what the hell he was doing now, he could actually trace more than at most three over the course of the night without keeling over, and because of that they were making great progress.

"Alright Shirou." Kitsirugu nodded, pleased with the boy's dedication to his practice. "Now that we are done with your foundation training, I am going to teach you a bit about bounded fields."

"You mean like that magic security system you have set up around the house?" The boy tilted his head to the side curiously. He was a bit winded from his training so far, however his somewhat large number of now activated magic circuits had quickly replenished his energy.

Kiritsugu nodded. "Correct. A Bounded Field is a topographic type of Magecraft, or in layman's terms a spell spread over a given area. To make one you have to in a sense knit a network of prana and spread it on base area, such as a piece of land or a building, to create a mystic boundary line that separates the "inside" from the "outside". The clearly advanced ones cover literal spaces, be it in mid air or underground, however that is something beyond what I can teach you." He scratched his head sheepishly. "You know I'm unable to use much magic anymore, however I was rather good at setting fields up, and especially good at tearing them down. The one around the house for example is almost impossible to detect even by strong mages since it does not attack or defend, but simply informs us of when someone with ill intentions comes inside. This includes humans and non humans which is somewhat rare for bounded fields."

Shirou's eyes however did not seem disappointed in the man in the slightest. "Cool! I knew you were awesome at this stuff!"

"Right…" Kiritsugu laughed nervously, knowing that all he was teaching the boy was stuff he could only remember since he had barely any text books on hand. "Anyways, bounded fields are what pretty much every magi use to protect their workshop. There are two general ways to make an effective defenses. The first is to make the fields you construct so subtle that the invading magi won't detect them and their effects until it is too late, and the other is to make the fields so overwhelmingly strong that they can overwhelm any offense that the enemy can think of." He smirked lazily. "I have a different approach in using and looking at magic compared to other magi, so I was pretty good at finding the weaknesses in strong fields. I once broke through a very strong set of fields around one noble's homes in a few hours. That said, I'd guess it would take even a strong magus to do the same about a year the conventional way."

He was somewhat embarrassed and ashamed that the boy looking at him in awe since he was pretty much bragging about how skilled he was at mystical breaking and entering. He prayed that this wouldn't leave the kid with ideas in the future.

"So then." He coughed and getting back to his lesson. "Once made, the boundary line will limit the range of the powers of the bounded field, but it is possible to set magic sigils across a the inside of the field to expand the area of effect, strengthen it, and do other things. A magus can erase the sigils of course as long as they know what they are doing. Similar results can be made by influencing the boundaries themselves by interrupting and removing the prana directly fueling it, so long as you know that the field is there and that you have the knowhow and prana yourself to do so. Some stronger fields are nearly impossible to destroy alone since they require certain methods, or they rely on a nearby prana "battery" to support it."

Kiritsugu paused for a moment as he saw Shirou blinking at him. It was at this point that he remembered that he was talking to a ten year old. He might have accidentally overwhelmed the kid with all the technical talk…

"So… basically." The boy said slowly. "You draw a shape with magic, and depending on the spell and how much prana you put in it you get different strengths and effects." He began to put the lecture into simpler terms. "Then you can make the field better with those rune things, but the runes and the field can be removed by a guy who knows what they are doing, and they will usually try to get rid of the runes first because it makes things easier for them."

Kitsirugu nodded. "Yeah. The guys at the Clocktower would use more complicated words, but that's the gist of it." He sat down casually. "For now though, let's get back to your training. First you have to learn how to make the lines to shape your bounded fields. Now close your mind and access your circuit. Most fields are rather big, but for now we are just going to focus on making a small circle around the both of us…"

o. o. o.

It had been two months now and Kiritsugu was fairly certain he had more than enough information on the future war to start preparing for specifics now. He was aware of the identity of every Master and Servant fighting in the war. Their powers, strengths, weaknesses, Noble Phantasms, personalities, desires… everything was written down in his notebook with as much detail as he could. He had no doubt that some things would change from how they were now. The war could start at an earlier or later date for some reason. Different masters or servants could be participating.

He had thought of a list of factors that would be present in this current war though.

Shirou would for certain summon Arturia again. The boy possessed Avalon, the sheath of Excalibur inside his body after all. The Grail was not a living being and had no consciousness, but with the constant presence of a potential Master and a strong catalyst was too convenient of an opportunity to pass…

The Master for the Tohsaka family would obviously be the daughter of Archer's original Master in the Fourth War, seeing as she was the only one in her family with the name and ability left. Who she would summon on the other hand was now up in the air though, as Kiritsugu's training of Shirou would have no doubt complicated things on that end.

However… should the Heroic Spirit Emiya be summoned once more… he should prepare something just in case for that…

If you spot this narrative on Amazon, know that it has been stolen. Report the violation.

The Master for the Matou family would likewise be the sister of Rin, the adopted girl Sakura, whose body was perpetually violated with crest worms, and her mind and body being corrupted and defiled by the remains of the previous Grail. The girl was the definition of a wild card at this stage, posing as a great threat or ally either way. Especially with Zoken still around. His best bet was to nudge the boy into archery club in middle school since they both apparantly attended it in the future, and likewise push him in her direction with a few suggestions afterwards should he still be alive at the time.

Still she was a difficult card to guide, maneuver, or control. It may be best to take a more permanent route depending on how things ultimately turn out.

The Master of the third of the great families that created the ritual would be… his daughter, Illiyaseviel Von Einzbern. The thought of which both flooded him with dread and joy. Putting the girl into a free for all war of legends that would most likely kill her, ironically was also the best bet he had at separating her from the oppressive magus family.

He had no doubt in his mind as well that her partner would be the Berserker of the war in the form of the legendary Heracles as well. The Einzbern family was always very thorough in their attempts in obtaining strong servants by finding the appropriate catalysts to summon them through. He could attest to that first hand when the family had delivered to him the genuine long lost scabbard of Excalibur itself so he could summon King Arturia as Saber.

It was almost a shame he had seen what the fate of the legendary demigod had become in each of the three main timelines. Heracles truly was the mightiest of Servants in this war, even if his mind was no longer present.

Then there was Kirei Kotomine. Kiritsugu had no doubt that the despicable priest would somehow make himself a part of the war in one way or another, secretly manipulating things from behind the scenes. The Golden King of Heroes was not much better, flaunting his power as soon as he saw it appropriate. Kiritsugu knew that making a move against either one of the two before the time was right was the equivalent to suicide.

Kirei and Gilgamesh… well there was more than enough to say about them. Thankfully though, it seems as if Kirei at least seems to want to stay back and watch for the time being.

Speaking of the uncertainties however, there were more than a few that had him unnerved to a degree. The first of which was the identity of Archer in this oncoming war. Having the future version of his son would be an immense boon to his efforts, but the unfortunate man would most likely be more interestid in trying to kill Shirou in an attempt to create a paradox and not be a Counter Guardian any more. If another Archer appeared… well Shirou would just have to deal with that when it happened.

The Matou family in general was another wild factor. Keeping Sakura alive with the possibility of becoming a dark grail was a very big risk. One he really didn't like. Zoken was just as bad, being a withered old demon barely in the shape of a human.

That did not mean however that he had not prepared plans with them in mind.

The identities of the Servants Lancer, Caster, Assassin, and even Rider were uncertain to him at this point. He was aware of who they were in his visions, but he had little guarantee that they would remain so in the future. He did not know who their original Masters were, save Riders, and if different catalysts would be used due to his interference. For now though he would just have to assume that they indeed were the ones that would eventually be summoned and hope for the best.

Kiritsugu had already formulated several plans for the battles, each one depending on certain factors and possible outcomes of steps that occur. Some were more important than others, yet the end result and the main goals would be the same:

The Grail war would end.

Ilya would be saved.

Shirou would not die.

As few innocents would die as possible.

What happened to the rest of the participants was really up to the heavens and how things turned out. He had given, most of them at least, a chance in his plans to survive, but their survival was up to them and a roll of the dice in the end.

Shirou had been getting the hang of his training for a while now. He had begun to practice his Projecting in earnest in addition to his Structural Grasping training. When Taiga was around the two would practice sparring in the dojo, much to his amusement and the boy's reluctance. Shirou in the mean time still went out of his way to help others in school without asking for any compensation even though he's only in fifth grade…

The base for the boy was there now. So long as he kept in those habits he would at least be in satisfactory condition for when the war comes. Kiritsugu had no doubt that should Counter Guardian Emiya still somehow be summoned as Archer, Shirou would no longer take so long to inherit and adapt to the man's memories physically or mentally.

Still… that was not enough to ensure victory by a long shot. A few years of slightly specified training for a boy going into his teen years would not protect him from an experienced magus, let alone a Heroic spirit. Shirou's abilities would not be able to pose a significant threat unless he laid eyes upon a Noble Phantasm, or at least trained to project Avalon, and that was still years from now. Years the former assassin did not have.

The boy needed an ace before the fighting even started.

After much debating, planning, and experimenting a small amount with the boy's Projection abilities a week earlier… Kiritsugu had come up with a solution.

He hoped his son would forgive him for it eventually.

"Are you going again?" Shirou moaned as his father closed his bag filled with clothes, notes, and a small wooden box.

"Yes." The father smiled gently, knowing why the boy was so down trodden. He tended to be gone for spans lasting almost a month at a time whenever he left in his attempts to rescue his daughter. Unfortunately his efforts were constantly stopped by either the Einzbern's guards or the barriers surrounding the isolated castle that took forever to get to and from.

They never bothered to listen to his warning that the Grail was corrupted by the spirit of Angra Mainyu. The embodiment of all the evils in the world.

A small smirk appeared on the man's face. He wondered if they still had that computer he had set up in the middle of their cathedral. He remembered how irritated he had made the elder of the family, bugging him about how it would increase his chances of victory in the 4th War if he had it until he had finally given in.

Odds were that it was utterly destroyed upon word that he had betrayed them. Oh well. The newer models were much better than the one there anyways.

"Is it the same place as always?" The boy asked with a sigh, already resigning himself to the fact that his dad would most likely be gone for a long time again to a place that he was never told.

"No." The father shook his head. "I have some business I have to take care of elsewhere this time. I should still be gone for a while, but not nearly as long as I normally am. Be good and keep Taiga-chan out of trouble." He patted the boy gently on his head, knowing exactly what he had just said. "Keep to your studies and your routine. Don't try any difficult magic while I'm gone other than your Projection, small bounded fields, and reinforcing objects. If you can show me some improvements when I get back, I'll start to teach you how to reinforce your body…"

Shirou's eyes widened in awe and excitement. Reinforcing a living body was exceptionally difficult and dangerous for most magi to do. That said, done properly it had some very interesting results, including but not limited to enhanced strength, speed, and sight. It was one of the first things the boy wanted to try to do when he learned about the spell, and as such it was of course one of the first things Kiritsugu had forbidden him from doing.

"Really!?" He asked excitedly, no doubt wondering about all the things he could do to secretly help people once he learned it.

The man nodded with a kind face. "Yeah, but you have to show me how much you've improved, and not die, when I come home."

Ah the life of a Magus. Your research was so likely to kill you at times that at times it truly was difficult to tell if one was joking about such things.

The boy nodded with vigor. "Yeah! Just you watch! I'm gonna project something awesome for you when you get back! And it will work too!" He looked at his dad with conviction.

"Well then I better make sure to have something else good to teach you as well when I get back or else I might run out of things to teach you." Kiristugu laughed as he began to walk out of the house. "Stay safe Shirou."

"I will!" The boy responded from the door. "Where are you going anyways?"

The Magus Killer had half a mind to leave the location of his trip a secret, however in the end he decided to tell the boy anyways. Unlike the Einzbern's castle, Shirou might actually go there at one point in the future when all this was behind him.

"England." Was all he said before closing the door behind him.

o. o. o.