On the eve of the expedition to Ireland, one day before departure.
With every preparation complete and the soldiers fast asleep, Artoria Caster walked soundlessly through the corridors of the quiet North Wales Castle.
Her steps were imbued with fairy concealment Magecraft, so neither the castle guards nor those sensitive to the slightest stir sensed her approach.
Her sole destination was the bedroom of her beloved brother, Kay.
"Heh heh. Everyone must be exhausted from prepping for the expedition and fast asleep by now. Artoria X is probably snoring away too. While they've all passed out, I'll sneak into Brother's bedchamber and have those tender arms all to myself."
Artoria Caster approached Kay's door, her mind dancing with devilish, sweet fantasies. Just as she began to pick the lock with a flick of her fingers and turn the doorknob…
"…Ah! M-Master! Brother♡!!"
Through the crack of the door spilled a woman's moans, impossibly coquettish and beastly.
Startled, Caster froze and stifled her breath. Peering through the slightly parted door, she stole a glimpse inside—and at that moment, she couldn't believe her eyes.
"Ughh! Ah, no, Brother! If you keep thrusting in so roughly, I feel like my mind will go spinning…♡!!"
On the massive bed inside the room.
Ordinarily clad in jet-black armor and striding the battlefield with high pride as a member of the Wild Hunt, Artoria Lancer Alter lay completely broken, sprawled like a defeated beast.
Kay, boasting an overwhelming physique and muscles honed by Scáthach's hellish training, had taken position behind her, panting heavily as he drove into her with relentless force.
From the normally proud Lancer Alter's lips came…
"I yield! I am wholly yours! Please, Master, do more with this sow!!!"
With that shameless declaration of defeat, she kept calling him Master and Brother, begging with polite speech without pause.
"Haah… haah."
Swallowing hard as she watched the scene unfold, Caster felt her cheeks burn. In the fairy's clear eyes, a deep lust and a strange sense of rivalry ignited.
At last, pushed beyond her limit, Lancer Alter let out a long scream and collapsed face-down onto the bed.
Her eyes half-rolled back, she lay exhausted with her face buried in the sheets, gasping for breath. She was completely unconscious.
"…Phew."
Kay brushed damp hair from his forehead and let out a deep sigh. His endurance and masculinity, honed by Scáthach's hellish training, far surpassed any common expectation.
He thought that to be truly satisfied he'd need at least two—or three—partners at once, and even his current harem was just within his limits. Of course, if Tamamo's bedroom arts were thrown into the mix, he'd handle it with ease.
"Damn it, she talked a big game about taking everything, but she conked out in no time. She's way too inexperienced… When it was too many, it was a problem, but when it's just a few, it's still an issue. Scáthach, what did you do to my body?"
Kay grumbled in dissatisfaction. And that was when...
He absentmindedly turned his head toward the door, and through the crack, his eyes met Caster's exactly as she peeked inside.
"Huh? What are you doing there…?"
Startled, Kay fumbled awkwardly, bending to pick up his clothes from the floor to dress himself. But Caster didn't flee.
On the contrary, she stepped into the room wearing a composed, seductive smile.
Click.
Locking the door firmly behind her, Caster leaned her staff against the wall and began slowly removing her cloak and garments.
By the moonlight, the fairy's white, smooth naked form was revealed. Without hesitation, Caster climbed onto the bed.
She gave the still breathless Lancer Alter a shove with her foot, sliding her aside into a corner of the bed, then straddled Kay's broad lap.
"Let me make up for what Alter couldn't give you—I'll fill you all night long."
Their eyes locked in sticky desire. Kay let go of his clothes and, as if entranced, wrapped his arms around her waist.
Soon, instead of his tyrannical grunts, the room filled with the fairy's sweet, sultry breaths.
How long their fierce encounter continued, no one could say.
Finally, at the height of her ecstasy, Caster trembled and collapsed into Kay's embrace. But something about her condition seemed off.
"Aaah…♡ I've lost! This Caster has been utterly defeated by Brother…♡ From now on, I belong to you forever, Brother♡"
After that bout...
"Where on earth did you learn to do that?"
At Kay's incredulous question, Caster let out a soft chuckle and returned to her usual innocent countenance.
"Heh heh... Surprised? I once picked up some fascinating manuscripts when I fell into another world as a changeling. When I translated them, I found that people in that world call them erotic doujinshi."
"…What? E-erotic doujinshi? You actually read that stuff?"
"Of course! In those, the heroines who submit to an incredible man like you always make expressions and poses called ahegao double peace. What do you think? Weren't you quite turned on?"
At the fairy's innocent yet depraved remark, Kay pressed a hand to his dizzying brow.
"You… you pretend to be the most innocent but are the darkest inside. And what about Alter, who let herself get corrupted without even looking at that stuff? So… you still have those things?"
"Oh? Interested? Come to my room later, and I'll show you."
Caster gave him a seductive wink and threw her arm around Kay's neck again.
"Now, enough chit-chat. Brother, do you know it's still hours until dawn?"
Thus began round two. By the time even Caster was left utterly spent and frothing, the beasts of Kay's chamber continued their night-long ordeal until the morning sun rose.
The next morning, the troops assembled on the castle's parade ground for departure. The knights, freshly arrayed, cut imposing figures as if nothing had happened last night.
Yet a strange atmosphere flowed among the knights' leadership.
There was Kay, looking just a bit tired but oddly refreshed; Caster, radiant enough to glow; and Lancer Alter, leaning against the battlements with an inscrutable, wickedly satisfied smile.
"…Hmph. It seems quite a grand spectacle went on last night. The stench still lingers."
Lancer Alter, having noticed everything, crossed her arms and sniffed in displeasure. Tamamo, Medusa, and Jeanne d'Arc Alter each nodded as if in acknowledgment.
But there was one among them who noticed nothing.
"Brother! Did you sleep well last night? Judging from the dark circles under your eyes, you must be tense at the thought of departure! Fear not, for I, Artoria X, will protect you perfectly by your side!"
Only the bounty hunter Artoria X, cheerfully making a blunder, linked arms with Kay. Kay broke into an awkward smile, a cold sweat on his brow.
"Hm? Things feel a bit different, don't they?"
And even Britomart, still a maiden, hadn't noticed—but if Artoria Lancer, readying for departure as the king, had seen this, she would have caught on.
Then Artoria Lancer ascended the dais and issued the deployment orders.
"The only troops being mobilized for this expedition are the Second Order of North Wales Knights."
The mobilization force was more modest than expected. Lancer calmly explained,
"The First Order of North Wales Knights will remain to defend the castle, and the Third Order of North Wales Knights must recover from the casualties of the recent skirmish with the Pict remnants. No matter how important this expedition is, we must not forget that North Wales itself is the frontline that can be invaded at any time."
North Wales stood between the kingdoms of Ireland to the west and the Pict invasions from the north. While there was no current threat from the Saxons, there was no guarantee that such an invasion would never occur.
At Lancer's words, Lancer Alter stepped forward, her face brimming with dissatisfaction.
"Hold on, you're the king heading out—why are we the ones left to defend? I'd like to slay the Irish giants and then enjoy a date with Brother on the Ehangwen."
Lancer Alter's sharp protest.
It was decided that Artoria Alter and Lancer Alter would remain at the castle, just in case. The decision was made by rock-paper-scissors, and Servants were excluded because even if they stayed away from Kay, they would still be within Britain's borders.
But in a surprising turn, Lancer Alter, who would normally rampage, looked infinitely gentle and patted Alter's shoulder soothingly.
"Ah, don't be so angry, Alter. What choice do we have if the king goes? If we stay behind and protect the home properly, Brother can fight and return with peace of mind, right? Heh heh."
Having been physically humbled by Kay in every way and lavished with boundless affection last night, Lancer Alter was in a state just shy of enlightenment, seeing all of creation as beautiful.
Seeing the normally warlike tyrant suddenly acting like a benevolent nun, Artoria Alter shuddered and rubbed her arms as if chilled.
"…You crazy bitch. What happened to your brain overnight?"
In any case, the troop deployment was complete.
With a great roar of magical energy, the massive cruise airship Ehangwen, outfitted with a grand banquet hall and cannons, appeared above the skies of North Wales.
Once Kay, Artoria Lancer, Artoria X, Artoria Caster, Britomart, the Servants, and the Second Order of North Wales Knights boarded, the Ehangwen set sail across the sea toward Ireland.
But at that very moment, as the North Wales party soared into the skies with hopeful hearts...
On the rugged plains of their destination, Ireland, a harrowing despair unfolded, leaving no shred of hope.
Kwaaang!!!
Against the ashen sky heavy with storm clouds, a bolt of lightning descended, triggering a tremendous blast.
Arthégal, the hero raised by Astraia, the goddess of justice.
He was covered in blood from head to toe, gasping for breath.
"Huff... huff! How... how could such a monster…"
Arthégal looked forward with despair in his eyes.
Through the whirlwind of dust and blood, a colossal knight clad in black iron walked steadily toward him. He was the tyrant of Ireland, the world's smallest giant, Grandotte.
Grandotte had dodged the lightning bolt unscathed. He watched Arthégal's stance, predicted where he'd land, and avoided it.
From his compact 2.5-meter frame, muscles coiled like springs, radiated a raw physical oppression that overwhelmed the god's disciple, Arthégal.
"You really thought you'd get hit by such an obvious attack, child of the goddess?"
Grandotte's cavernous voice echoed across the plain. In his hand, the enormous poleaxe, its head studded with crude iron, was slowly raised skyward.
"If this is the caliber of the vanguard sent by the Fairy Queen Gloriana, then Britain's future is equally predictable. Still, you fought well. You're the first to inflict this level of damage on me."
"Grrraaaaargh!!"
Gathering all his remaining strength, Arthégal charged forward, swinging the golden sword Chrysaor. But...
Thwack!!!
No flashy magic or fancy technique—just raw, brutal force as Grandotte's poleaxe sliced through the air and shattered Arthégal's torso.
His helmet and breastplate were torn apart like paper, and the hero's blood stained the cold Irish earth.
Arthégal, the goddess's nurtured hero, met a cruel and futile death moments before Britomart could arrive.
Grandotte slung the blood-dripping poleaxe over his shoulder and fixed his malevolent gaze across the sea toward Britain.
Was this the butterfly effect?
Was it caused by Kay's presence, or the culmination of countless intertwined fates?
The hero who was supposed to vanquish Grandotte alongside Britomart and King Arthur, become a legend, and sire the king who would lead post-Arthurian Britain—
...in the end could not become a hero and met his death.