Saber's wish is to use the Holy Grail to choose a different king. She's come to believe she wasn't fit to be king herself.
If a new king were chosen, maybe the kingdom wouldn't have fallen—at the very least, it wouldn't have collapsed the way it did.
Whether or not Shichen has fully persuaded her yet, she's certain that putting someone else on the throne would have led to a different outcome.
She still doesn't want to see her kingdom destroyed.
That's the main reason she became a Heroic Spirit in the first place.
She's determined to realize this wish no matter what—though the urgency isn't as fierce as when she started.
Shichen's words did get through to her; she understands now what he meant about her "savior complex."
"Saber, have you never doubted the Grail?" Shichen asked.
"Doubted what?" Saber looked at him, puzzled.
"Do you really think the Grail can grant any wish?" Shichen held her gaze, serious.
"What are you implying?" Saber's face tightened.
"Come on—if it could truly grant any wish, do you think the Grail would still exist in this world?"
"…Right."
Saber finally followed the logic: if the very first winner had actually obtained an all-powerful Grail, why would anyone else ever be allowed to get it again?
If the Grail really could do anything, the greedy and the reckless would have used it for unthinkable wishes—and once those came true, there'd be no 'Grail' left to fight over.
But that isn't the crux of it. As Shichen remembers, the Grail itself has no mind or judgment. It's just a container filled with a massive amount of colorless mana. All it can do is supply power in line with the user's wish.
The "how" is up to the user—the method and process must be specified.
In other words, if the user knows the magecraft needed to realize a wish, the Grail can provide the juice to make it happen. If the user doesn't know how to realize it with magecraft—or if the wish itself lies beyond magecraft's scope—then the Grail can't deliver.
Because the mana inside the Grail is not infinite; it cannot do everything.
"Do you see the Grail's limits now?" Shichen asked with a small smile.
"Mm… I do. But my wish—the Grail should be able to grant it, right?" Saber asked, anxious.
"That part isn't the problem."
Saber's expression brightened—only for Shichen to cut in before a second passed.
"But I won't let you use the Grail to make that wish."
"Huh?"
Saber stared at him, stunned. "What… do you mean?"
"Relax. I'm not turning against you," Shichen said, ruffling her hair.
"Then what are you saying?" Saber let out a quiet breath of relief.
She hadn't been afraid he'd fight her; she'd been afraid he'd been lying to her.
They sound similar, but to her right now, they're worlds apart.
"Next, I need to tell you the real reason I came to this world."
"Came to this world?" Saber caught the key phrase, frowning.
"I'll explain that after. First, let's talk about the Grail."
"The Grail?"
"It's been tainted," Shichen said, his expression turning grave.
"Tainted? What does that even mean?"
Saber could only follow his lead, still not understanding.
"You know there have been several Grail Wars already, right?" Shichen asked instead of answering directly.
"Mm… This is the Fourth Holy Grail War," Saber nodded slowly.
"The taint happened during the last one."
"Shichen, what are you getting at?"
"Don't rush. Hear me out."
Shichen began to explain what happened in the Third Holy Grail War. He hadn't lived it himself, but he remembered it clearly.
During the Third War, the Einzbern family broke the rules to pursue their goal and summoned a so-called 'eighth class' Servant—Angra Mainyu.
They'd hoped to call forth a powerful evil god. Instead, they summoned an ordinary man, who was defeated on the fourth day after the war began. Worse, Angra Mainyu's soul was absorbed into the Grail.
That's how the Grail was corrupted—because of Angra Mainyu's peculiar nature.
He'd been an ordinary youth whom his village treated as a sacrifice to a false "god," a vessel onto which they projected humanity's malice.
After he was summoned and defeated, the Grail mistook that malice for the collective "wish" of mankind and tried to grant it.
But those "wishes" are evil. A tainted Grail becomes uncontrollable. Once released, it will spew forth "All the World's Evils"—Angra Mainyu—bringing endless calamity and ruin.
That malice won't stop until every human is dead.
In other words, any subsequent wish would be twisted by that malice—leading, ultimately, to humanity's extinction.
"That's impossible…" Saber said after listening, unwilling to accept it.
If that's true, what's the point of her fighting in the Grail War?
Wouldn't her wish be ungrantable?
And even if it could be granted, it would carry a terrible price—because of her, the human race might be wiped out.
That's the last thing she wants.
"You don't believe me?" Shichen asked calmly.
"I…" She paused, then shook her head. "How could I not believe you?"
He had no reason to lie, and he'd been thinking of her from the start. If he wanted to stop her from making the wish, there were easier ways—he wouldn't need to spin a story like this.
And that made it even harder to accept.
She'd come this far, finally close to making her wish come true—only to end up with nothing.
Though, if she was honest, she hadn't exactly done much herself.
"Hey," Shichen murmured, pained, pulling her into a tight hug.
Honestly, whether Saber realized her wish didn't matter much to him; it would "only" rewrite history. Even if this world's history changed, he could still take everyone and leave—including her.
After that, this world would no longer concern them. Saber and the others could start fresh, without regrets.
But with the Grail corrupted, regret felt inevitable.
"So I really… can't have my wish?" Saber whispered into his chest.
"You can—if you don't care about the lives of everyone in this world."
"…What?"
"You might not realize how the Grail misreads wishes. If you ask it to 'choose another king' and change history, it may erase everyone to accomplish that."
"How could it—"
"It really would."
"…Why didn't you tell me earlier?"
"Back then, we weren't this close. If I'd told you then, would you have believed me?"
"I…" Saber had no answer.
She knew her own obsession. If he'd told her earlier, she never would have believed him—and it might have wrecked their relationship.
And Shichen would never harm her. If, in the end, she ignored him and still made the wish… she'd be the greatest sinner of all.
"What… what should I do?" Her voice wavered, on the verge of tears.
"What?" Shichen blinked.
"What am I supposed to do now?" Saber suddenly wrapped her arms around him and curled into his embrace.
"Simple. We destroy the Grail," Shichen said, gently patting her back.
"Destroy the Grail?" Saber looked up despite herself, eyes blurred with tears.
Shichen cupped her face and wiped the corners of her eyes with his thumb, smiling softly. "How could we let a Grail like this remain? Sooner or later it will harm this world. Let's end it."
"Destroy the Grail… Is that—that's what you meant? The reason you came to this world?"
"Not the only reason," Shichen said with a smile, shaking his head.
"Huh?"
"To meet you."
"W-what…" Saber murmured, asking on reflex.
"The real reason I came to this world was to meet you all."
"…Who are you, really?" Saber felt like he had to be joking.
"I'm Shichen—Illya's father, Sakura's Onii-chan, Iri's lover… and the man who likes you."
"Can you not joke around?"
"How could I joke at a time like this?" Shichen met her eyes, sincere.
Saber realized he probably wasn't joking—but she couldn't handle a confession right now. Her thoughts were a knot.
It suddenly felt like the Grail War had lost all meaning to her.
She didn't respond. She lowered her head, at a loss.
"Why… did I even enter the Grail War?"
"You don't know?" Shichen asked.
"Know what?"
"You became a Heroic Spirit and joined the war to meet me—to become my Servant."
"That's impossible…"
"Why not? Make it your new goal. Start a new life for yourself. Your regrets are already history—let them go."
"How could I ever for—mmph!"
Saber's protest was cut off—by Shichen's fierce kiss.