Artoria looked at the two sides facing off and quickly distinguished friend from foe.
Without hesitation, she stepped in front of Xia Yu, leveling her Invisible Air at Cu Chulainn.
"Stand down, Lancer!"
"Tsk, barging into someone else's battlefield uninvited," Cu Chulainn said irritably. "Do you have no manners at all? Can't you see we were right in the middle of enjoying ourselves?"
"Enjoying yourselves? Does bullying a civilian bring you that much pleasure?" Artoria deliberately used a provocative tone.
"A civilian?!" Cu Chulainn was momentarily stunned by the remark. "You saw our fight, didn't you?"
"A 'civilian' who can suppress me in martial arts? You've got to be joking!"
"But she is not like us, who have manifested as Servants," Artoria replied calmly, following her own rigid logic. "Even if we are defeated and die, we simply return to the Throne of Heroes. She is still alive!"
"She is so young and has so much ahead of her. Therefore, until I fall, I will not allow you to continue your assault on her."
"Hey, hey, hey, this is the Holy Grail War," Cu Chulainn's lip twitched. "How can you be so naive?"
"It is not naivety, but a respect for talent," Artoria shook her head. "I know this is a battlefield where one risks everything, and I am willing to stake my own life. But there are some things that, once seen, cannot be ignored."
Indeed, she spoke out of a genuine appreciation for the girl's skill, using the provocation to draw Cu Chulainn's attention solely to herself.
What an incredible helper—and an ally at that—to be able to pressure a Heroic Spirit like Lancer. She couldn't let her come to harm here. No matter how powerful her combat techniques were, there was one gap that could never be bridged by skill alone.
The Noble Phantasm.
In Artoria's view, the moment the opposing Lancer unleashed his Noble Phantasm, the girl's defeat would be a mere matter of time.
"Judging by your appearance, you were just summoned, weren't you? Tsk, I knew that kid was trouble," Cu Chulainn swept a gaze over her. "How could a normal person come back to life after I killed him?"
"And that armor of yours—a knight? Just jumping into someone else's fight like that?"
Since the talk had turned into a war of words, he, as a Heroic Spirit, was more than happy to play along.
"King against king, general against general," Artoria was unmoved. "I am your opponent. Furthermore, how is this 'interrupting' a fight?"
"Do you really intend to keep going? You were the one who backed away. Don't tell me you didn't notice the pair in the distance or the Bounded Field in the shadows."
"I noticed, obviously. It's just... it seems you're the one who hasn't grasped the situation," Cu Chulainn raised an eyebrow, spinning his spear casually. "Do you really think the person behind you is on your side?"
During the fight, he had sensed it. Although the girl protected that kid, the Servant actually providing support was Caster. Even if this girl wasn't a Master, she was inextricably linked to Caster.
Combined with this newly summoned Saber, it was likely that the person behind the scenes hadn't even foreseen this development.
"Tsk, tsk, tsk. Interesting, very interesting. Hey," his gaze bypassed Artoria and landed on the woman calling herself Firefly. "Can I ask? How does it feel?"
"The kid you were protecting just moments ago has turned into an opponent in the blink of an eye. If I were you, I'd run that woman through right now to eliminate one threat. At most, you could just let the kid live."
"What?" Artoria was slightly dazed. Hadn't she been told the person behind her was an ally? Was the intelligence wrong?
Just then, an arm wrapped around her neck.
Artoria hadn't even sensed the movement. Her body stiffened instantly, and she instinctively moved to break free.
To her surprise, the arms were incredibly powerful. Even for her, it was difficult to exert force while her neck was restrained.
She couldn't exactly swing her sword backward either, as this might be Lancer's attempt to sow discord, and the girl behind her truly radiated no hostility. If she really was an ally, a strike would be disastrous.
She could only look toward the gate, hoping her Master would appear soon and give her an answer.
At that moment, the girl behind her spoke.
"No need for the petty provocation, Lancer," Xia Yu leaned in and nuzzled Artoria's cheek. "I really like Saber. Backstabbing? Impossible."
If I'm going to fight, I'll do it head-on. With my abilities, why would I ever need to backstab?
"I knew that if I stayed by Emiya's side, I'd eventually run into you."
"Oh? Is that so?" Cu Chulainn's expression was full of hidden meaning.
He didn't believe a word of it.
After all, the girl had called out his True Name the moment they met, yet now, in front of others, she called him Lancer.
Heh.
Only a fool would believe there wasn't something fishy going on.
"Let go of me first," Artoria said, feeling entirely out of her element. She had rarely experienced such intimate contact, and being held in a double-armed embrace made her extremely uncomfortable.
"I cannot fight in this position."
"Fight? No, the fight is already over," Xia Yu looked up at Cu Chulainn. "Do you think he'll still attack facing both of us? Not to mention there are others watching."
"Lancer, I'll tell you a secret. You killed that kid once, but do you know how he came back to life?"
"It was that pair over there. Tsk, tsk, tsk. That Emiya kid is surrounded by girls; someone paid a heavy price to bring his little life back."
"Take a guess—if you stay here, will you end up being mobbed?"
"...It seems I'm the odd one out," Cu Chulainn glanced at her and then at the motionless duo in the distance, not doubting her words.
He had killed the boy at the school, so the only person who could have saved him at that time was likely the Master of the one he had been fighting.
"However, I can't just leave like this," blood-red mana condensed around Cu Chulainn like lightning, his power surging rapidly.
"My Master, you see, is a complete and utter scoundrel," he said, badmouthing his own Master without a care. "As a Servant, I have no choice."
He leveled the Scarlet Spear, visible mana gathering upon it.
"A simple scouting mission ending like this. Hah."
"Careful, it's a Noble Phantasm!" Seeing this, Artoria forcefully broke free from Xia Yu's grip. She stepped forward with her Holy Sword to ensure the girl behind her wouldn't be caught in the blast, standing ready.
"Gáe Bolg!"
The Scarlet Spear shot toward the two like a bolt of lightning. Artoria tracked the spear's trajectory and released her mana, raising her sword to intercept!
But to her shock, the Scarlet Spear took an impossible turn right before her, curving past her body to strike at the person behind.
"What?!" Artoria's eyes nearly bulged out of her head. She tried to turn and intercept, but it was too late. Her vaunted Instinct seemed to have failed—was it because she wasn't the target? But it had never been like this before!
She could only watch helplessly as the Scarlet Spear, carrying massive mana, lunged like a bolt of lightning toward the girl's heart.
Xia Yu, however, remained very calm.
A teal glow flickered across her body. Under the threat to her heart, she was finally able to mobilize a sliver of the power she could usually only barely touch.
In her eyes, the lightning-fast speed of the Scarlet Spear slowed down. She simply reached out and caught the spear in her hand.
Then, with her other hand, she reached to the left and grabbed Emiya Shirou by the collar.
This guy was truly reckless. Instead of running when he saw a Noble Phantasm, he actually tried to rush over and take the hit for her. Then again, he was Emiya Shirou.
"This is?!" Cu Chulainn was shaken to his core. It wasn't that his spear had never been blocked before, but never in such an absurd manner.
This was Gáe Bolg, a Noble Phantasm for use against an army originally meant for throwing, which Cu Chulainn had personally adapted for use against individuals. It was his ultimate technique and trump card.
It was a strike that reversed the causality of the sequence of events. At the moment it was unleashed, the "effect" of the heart being pierced was created first, and the "cause"—the spear hitting the target—followed after.
Unless one possessed significant Luck, it was essentially a strike that guaranteed death upon release. Its mana consumption was low and its activation speed was fast; for such a powerful effect as almost certainly destroying the enemy's heart, it required remarkably little mana, making it a highly efficient Noble Phantasm.
Unless one had incredible Instinct and Luck, like Artoria, it was impossible to evade!
Xia Yu lacked both, but she possessed an absolute, overwhelming power level.
You want to pierce my heart to complete the causal loop? Then try breaking free of my grip first.
Under an absolute power level capable of launching attacks that could tear the surface of a planet, the mechanics of Gáe Bolg were negligible!
Ultimately, no matter how powerful an attack is, it must be maintained by mana. As the saying goes, "The poison is in the dose." If you had the nerve to fire the same move at Tiamat, you'd see if her heart would even notice.
If this Noble Phantasm were truly omnipotent, he would have been a Grand Class Lancer long ago.
In this situation, there were only two outcomes.
Either Xia Yu's strength would run out first, losing the ability to restrain the Noble Phantasm and letting it complete the causal loop, or Cu Chulainn's mana would be drained dry by the continuous activation, causing the Noble Phantasm to fail automatically.
The current situation was already quite clear.
Seeing this, Cu Chulainn sensibly deactivated the Noble Phantasm.
"I'm starting to doubt again—are you really not a Servant?" He put his spear away and looked at Xia Yu with a grave expression.
"Oh, I'm a Berserker," Xia Yu said, blinking.
"...Do you really think I'd believe that? You don't look like a Heroic Spirit at all," Cu Chulainn shook his head. "Let's call it a day. My cowardly Master seems to have been spooked."
"Or do you all plan on keeping me here?"
"Go on, get out of here," Xia Yu waved her hand. "The fight was fun today. When my hands get itchy again, I'll come find you."