Well, I feel I need to explain this, since it's important to understand my way of thinking at the time, as I won't be doing so in the following parts of the story.
During the Fourth Holy Grail War, Zouken took parts of the Grail and implanted them in Sakura, turning her into a less-than-ideal vessel, since it was a forced transformation. It's also worth mentioning that Zouken died due to Kirei's intervention with Sakura, but Dante doesn't care about the monster's life or death.
Meanwhile, this Illya is the Lesser Grail; by default, this is stated explicitly in the series.
So we have a corrupted Pseudo-Grail and a Lesser Grail taken and absorbed by Kirei. Basically, she becomes a much more dangerous version of Sakura, since her mind can't be distorted any further. She has the power to absorb Servants, almost infinite mana, and enhanced Executioner combat abilities.
Kirei, if he prepared well, might have had a small chance of fighting a Servant, but now, with all this, he can defeat almost any Servant. This is mainly to give you an idea of his power, and clearly, by default, he'll be very difficult to kill, since his ability to transform allows him to use the full power of the corrupted Grail at its maximum potential—hence his metamorphosis.
I'm not going to make the fight between Shirou and Rider against Kirei easy, as it would be boring, at least from my point of view.
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Day had already dawned; while the three sorceresses and a mage were maintaining the enclosed field to prevent its collapse, one of the four was watching the hourglass.
The hourglass showed halfway through the day, and soon the sand would be running out.
Just as the last grain of sand fell, Aoko immediately released her hands from the seals, destabilizing the entire enclosed field.
"What the...?" asked Rin, who had been on autopilot to make time pass faster, so she wasn't very aware of her surroundings.
Alice yawned, having gone more than a day without sleep and needing energy for what was coming.
"Let's see how much that brat has changed," commented Touko, walking towards Dante and the others.
Aoko was the first to arrive and looked at Dante, who was sitting resting against the wall of the shed.
"I see you finally broke the field; I was wondering when I'd get around to it," Dante said, getting up.
"Hmm, you haven't changed a bit," Aoko said, sounding a little disappointed.
"Did I expect you to change?" Dante asked.
"I don't know; I was expecting some change, yeah, I don't know, taller or more muscular or maybe horns." Upon hearing that, Dante could only look at her with a touch of disbelief. "At least that Emiya guy actually changed."
At that moment, the others arrived.
"You look different, kid," Touko commented, approaching Shirou, who had just stood up, as he had been waiting along with Dante.
Not far behind, Rin appeared with Sakura. Rin's mouth fell open in disbelief, while Sakura covered hers in shock.
"It's been a year and a half here," Shirou said, looking at the two young women. "Rin, Sakura, it's been so long since I've seen you."
Neither of them answered; they were somewhat agitated, especially Rin, who, from her perspective, didn't see Shirou but someone else—Archer.
Shirou appeared a few centimeters taller, with more tanned skin; white hair; a red chest, a vestige of his original color; and darker eyes; to put it another way, he was like the original, but duller.
"It was tough training; since I couldn't increase the quality and quantity, we had to be as efficient as possible, and it was based on overusing them to control their pressure along with their control," Dante began to explain.
"Master," Rider's voice was heard, appearing beside Dante. "You fulfilled your mission exactly as you requested: no one from outside entered the perimeter."
"Well done, I expected nothing less from you," Dante congratulated, stroking Rider's hair. If Rider had a dog's tail, it would be wagging, showing his delight at his master's caresses.
At that moment, Alice approached Shirou and began to examine him closely.
"Overuse of the magic circuits has left you like this; sadly, it's irreversible," Alice stated before going to sleep somewhere nearby.
"I know, but as the days passed and the changes in my body became more noticeable, along with Dante and Kiss-shot's help, I decided to accept the truth and move on," Shirou said.
At that moment, Rin stormed over to where the white-haired man now stood and repeatedly pressed her index finger into his chest.
"You…" she dragged out the words, glaring at Shirou, only to see him remain inactive and wait for her to act. She could only sigh. "You and I will have a word, but that will have to wait; I'm very tired. I'm going to bed too."
With that, he followed Alice to rest.
"Senpai, are you alright?" Sakura asked, acting as his caregiver.
"Yes, I'm fine," he replied simply.
"Well, I'm curious to know what you two did," Touko said to Dante.
"Yeah, me too," Aoko continued, clinging to Dante.
"Aren't you two going to rest?" Dante asked.
"I don't need sleep to rest," Touko explained, lighting a cigarette.
"And you know, if the situation calls for it, I can go days without resting," Aoko added.
Upon hearing that, Dante felt a phantom pain in his spine and hip.
"Well, it wasn't a big deal."
...
*Flashback*
Shirou was seen getting up from his faint, staring at the "supposed" wound on his chest, which was "healed," but it was as if nothing had happened.
"But what?" he wondered, noticing Dante staring at him with those blue eyes that had a certain metallic quality.
"Shirou Emiya has a very interesting history," Dante remarked, leaving Shirou confused. "There are some things I didn't even know you'd been through, like your transformation into EMIYA."
"What are you talking about?" the red-haired teenager questioned. You pierced my chest with your hand, then I felt pain throughout my body, and then what happened?"
"Hmm, let me explain. I possess one of the five magics, specifically the third, the same one used in the Holy Grail ritual." Shirou was astonished to hear this. "Basically, it's soul manipulation. That's what I did when I supposedly attacked you. I took your soul and gave you the same kind of power I have while modifying your body with alchemy to better suit this power; hence, the intense pain. For that, I had to use these eyes to see how willpower and Haki work in another person's body. Once I understood, I simply replicated it in your body."
Once Dante finished explaining, Shirou stared at his body, trying to see if anything was different about him.
With the alchemy fruit, he could repair and join body parts, so modifying certain aspects of his body using the supporting sorceress wasn't too difficult for Dante.
"So, am I ready for training?" Shirou asked.
"Almost," Dante replied, tossing him something. "Here, take this."
"What is it?" he asked.
"It's a pill. It will help eliminate impurities in your body and strengthen it. Think of it like those Chinese novels where con artists used pills to achieve immortality," he explained.
"Does that mean I'll be an immortal like you after all this?" he asked, somewhat excited.
"Don't exaggerate. I only have that one pill, and to make matters worse, I also have three types of immorality, none of which come from cultivation." With those words, they somewhat dampened Shirou's enthusiasm, since who wouldn't want to be one of those characters from Chinese novels who become invincible for no reason?
Dante possesses three types of immortality. The first comes from the Fountain of Youth, which prevents him from aging and becoming senile. The second comes from Kiss-shot herself; since their souls are bound together, they both need to die simultaneously; otherwise, they don't die. Dante may lose his body, but he will remain alive. The third is the one that grants him the third magic, dependence on body and soul; this means that, as long as the attack doesn't damage the soul, he can continue to exist without a body.
These immortalities are very similar, but they follow different concepts, so it can be said that they complement each other.
He also possesses a fourth immortality, but it only works if he is a vampire, which is almost infinite and immediate regeneration. If he doesn't transform into a vampire, it doesn't work.
"You mentioned my history; what do you mean?" Shirou asked.
"Well, these eyes allow me to see parallel timelines, but only to see them. To glimpse your full potential, I saw different Shirous from other timelines to see how they developed their abilities and how they got there."
"So, what did you mean by Emiya?" he asked curiously.
"It's better if I show you," Dante declared, activating the all-seeing Eyes of God to share his vision with Shirou.
At that moment, Shirou saw different parts of his alternate life, how he followed the path to becoming a hero of justice, and how that same path ultimately transformed him into the despised man, Archer.
With these rapid visions, Shirou collapsed to the ground, his head throbbing. He wasn't used to this kind of thing, nor to pain.
Dante had been very selective in showing Shirou the images, as he didn't want to distort or overwhelm his mind.
"I refuse," Shirou exclaimed from the ground. "I refuse to believe I'll become that man."
"You won't become Archer; you've already forged a different path. That doesn't change the fact that you're both Shirou Emiya."
After Dante's explanation, Shirou simply lay on the ground, lost in thought.
"You'd better take that pill and meditate; the sooner we start training, the better." With that, Dante left Shirou alone to meditate.
Shirou stared at the ground for a few moments before taking the pill and positioning himself, like a monk, to meditate.
*End of flashback.*
...
"I see," Touko concluded, "you used the parallel lines to nourish Emiya with knowledge and techniques."
"Yes, it was quite complicated, since I had to be careful not to fragment the mind and personality of the original Shirou, as the idea was that he wouldn't be lost or become a vessel for his other self," Dante added.
"Well, I'll go make something. It's been a while since I cooked, and I feel like my culinary skills are rusty," Shirou said, scouring the destroyed house for utensils and anything else that might have been salvaged.
"Let me help you, Senpai," Sakura said, following him, leaving the four of them alone.
"So, you still think you can't beat that guy with the golden weapons?" Touko asked.
"So, you still think you can't beat that guy with the golden weapons?" "It's complicated. I know Gilgamesh used his clairvoyance, so he must have seen something that made him act, or..." Dante explained, looking directly at Touko. "He saw everything and nothing at the same time."
"What does that mean?" Rider asked.
"He possesses clairvoyance like hers, but more powerful; he sees the future. I do too, but only for a few seconds ahead," Dante said. "If he sees the future and then I do it to change it, then Gilgamesh will see a different future, and so on, so his clairvoyance isn't much help right now."
Gilgamesh can't rely on his clairvoyance because it's constantly changing, since Dante also possesses one that will alter events every moment, changing the future.
The uncertainty of what will happen is what fueled Gilgamesh's determination to act and do things for himself, adding the variable that changes everything: Dante.
Dante was ruining the Holy Grail War by preventing any Servants from killing each other, something Kirei disliked. So, with Gilgamesh's help—Gilgamesh, eager for a thrilling fight to the death with the Greek god of death—Kirei decided to assist in his own way.
"But can't you catch him before he does anything?" Aoko questioned.
"That would be ideal, but while his clairvoyance might not be useful in the long run, it does allow him to see my actions in the short term. Yes, by the time I act, he'll likely have already done something, and I have no way to counter that ability or his most powerful weapon," Dante explained. "Since he wants to go all out, I don't know if I'll have time to attack before he draws that weapon. As soon as he sees he's in danger, he'll do it, along with Enkidu."
"Ideally, that would be the case." "But if I use all my power, both what I have now and what was sealed away, then I'll have a chance to kill him. But for that, I need the four of you to help me create the boundary. With that, I can guarantee I can kill Gilgamesh. Without it, it's very difficult, since he won't trust me."
At Dante's words, Aoko and Touko nodded.
"No problem, holding a barrette is a piece of cake," Aoko declared happily.
"I hope you can make it up to me for everything you're putting me through," Touko smiled, lighting another cigarette.
"Thank you very much," Dante said.
...
A few hours had passed since Dante, Kiss-shot, and Shirou returned, and the sun was already setting.
At the highest point stood Rider, the last Servant available in this war, protecting the area and, by extension, her master.
"Hey, Rider," a shout called out. She looked toward the sound and saw that it was Dante not far away, signaling for her to come.
She leaped and landed in front of him, displaying her agility; the fall was quite graceful, too.
"I see you've been pushing yourself, but you should rest as well; later you'll go with Shirou to stop Kotomine, who is the one we absolutely must stop. If it weren't for Gilgamesh's words, I would have sent Shirou against him, and I would have dealt with that nefarious priest myself," Dante told her.
"Don't worry, Master, I want to stay here watching in case any enemy reappears; that way you'll be ready to defend him and the others," Rider told him.
Dante stared at Rider, making her a little nervous.
"You've changed, though not too much yet," Dante complimented her, stroking Rider's head. "You've worked very hard and done very well."
Rider simply reveled in her master's caresses.
Dante's hand moved from her hair to her cheek, then to her chin, lifting her head and forcing her to make eye contact.
"During these years, I've thought about everything that's happened, both in this war and before," Dante began to recount. Not knowing your own emotions and how to express them, I thought that by making you understand them, that crush you had would fade with time, since things like this have happened to me before. But against my prediction, it didn't. And to be honest, someone like you also had a wish that I feel I've been neglecting all these days. So, when this is over, do you want to come with me and the others and spend the rest of our days on adventures together?"
Rider's eyes lit up at Dante's words.
"Of course! It must be an honor to have you by my side and join your harem, being the very reincarnation of the god of fortune," she declared, jumping at his neck and trying to kiss him.
"I don't have a harem," Dante complained at first, rejecting Rider, but in the end, he accepted her, accepting her completely.
Not far away, Kiss-hot was watching them; she just shook her head.
She had spoken with Dante during their time in the fenced-off field about... The topic of relationships and relationships.
I almost forced myself to bring it up, to be honest; with Dante, it's all about relationships. He has Medusa, Aoko, her, and now Kenshin.
Kiss-shot didn't care how many of Dante's partners he had, but she knew he wouldn't accept many or just anyone, not to mention that the bond she had with her husband was unbreakable, and she knew she would always be his first.
With that, Kiss-shot went to eat the food that Shirou guy made; she couldn't taste human food, but for some reason, she could taste what he made—another mystery of life to add to the list.
...
Night had fallen, and the groups were formed. Shirou and Rider would go to the Ryudou Temple, where the Holy Grail and, by default, Kirei were located. Meanwhile, Dante, along with Aoko, Touko, Alice, and Rin, would go to the forest of Einsbern Castle, where Gilgamesh and Saber were.
Kiss-shot would stay not far from the temple in case Shirou and Rider failed so she could move to Dante's location and warn him to escape, or in case her husband died so she could keep his soul away from that psychopath.
"Alright, everything's ready, but there's just one more thing," Dante said, looking at Rider and extending his hand. "By this Command Seal, Rider, I order you that, no matter what happens, you must fulfill your mission and resist any curse or impediment that prevents you from achieving your goal."
With that, Dante's final Command Seal was activated.
"Yes, Master," Rider replied, smiling.
Dante nodded.
"I trust you both; I hope everything goes well." Before these words, Rider and Shirou nodded. "Let's go."
...
Dante walked through the entire castle holding the AT, which had been modified over time within the designated area, making it more powerful and, above all, magical.
The others must be hidden at the edge of the forest, waiting for Dante to distract Gilgamesh so they can begin preparing the designated area.
Since it's a much larger space and they don't want to be discovered, it will take them longer to get it ready, giving Dante plenty of time to distract Gilgamesh before the real fight begins.
"I see you've arrived, dark entity," Gilgamesh's voice was heard as Dante entered the mansion's reception room.
There stood the king of heroes in his golden armor, while Saber was held to one side by Enkidu, unable to move; her eyes looked almost lifeless.
"You've come to accept my offer; with me by your side, you'll lack nothing, and I can even offer you some of my treasures."
"Hmm, if I ask you to give me Ea, would you accept?" he asked Dante.
Gilgamesh's smile vanished instantly.
"Who do you think you are?" he asked irritably.
"I see the negotiations are dead, and I don't have time for games," Dante declared, aiming his sniper rifle at Gilgamesh.
Gilgamesh looked at this and opened dozens of golden gates.
The AT filled with prana, while a magic circle appeared at its mouthpiece.
"This is one of my most powerful attacks; take it, king of heroes," Dante exclaimed.
"That won't hurt me one bit," Gilgamesh mocked, but he summoned shields anyway while pointing swords at Dante.
The AT's magical energy was at its peak, and just as it was about to fire, fully intending to kill Gilgamesh, its intentions shifted completely.
In a swift movement, it switched its aim from Gilgamesh to Saber.
"What?" Gilgamesh exclaimed upon seeing this. He had seen Dante fire, but the future had drastically changed out of nowhere.
"See you soon, King of Knights." With that, the bullet, infused with alchemy and magical energy, traveled at full speed.
Gilgamesh fired his weapon, but he couldn't control the shot.
Saber watched all of this and simply smiled as the bullet approached.
The shot pierced Saber's armor, destroying her heart and killing her instantly.
She began to fade away slowly until she was gone.
"You bastard, HOW DARE YOU?" Gilgamesh roared, opening thousands of portals.
"My gun slipped; it was an accident," Dante replied mockingly.
Elsewhere, Shirou and Rider had already arrived at the temple, but suddenly, the white-haired man felt his connection with Saber slipping.
"What's wrong?" Rider asked, seeing Shirou pause for a moment.
"Nothing, it's just that Saber is finally free, and that puts my mind at ease a little; let's keep going," Shirou said resolutely.
He knew about this. It was Dante's plan to free Saber from Gilgamesh's clutches. He wasn't worried about this, since Dante had told him that Saber's true body was on the other side of the world and that when this was over, he could bring her back to our world.
So he just had to do his part now, while Dante kept Gilgamesh occupied.