If you expect this to be serious, …
Go read something else.
The Lily War
Gilgamesh frowned as his clairvoyance materials inside the Gate of Babylon told him to use his Noble Phantasm and how to do so.
"This is most definitely foolish," he grumbled as he pulled out a cart of potion of youth from his treasury. "I am the greatest king. Why would I need to display my collection of potion of youth when I already know-"
Whatever Gilgamesh might have finished saying, we will never know.
Why? Let's go to another scene.
Archer froze on the roof of the Tohsaka mansion as he watched Gilgamesh, the King of Heroes out for a stroll. Completely undefended when the Grail War would soon be starting.
He couldn't believe his luck. Should he take this opportunity?
His younger self had encountered Lancer and himself this night already and he and his Master had retreated to home. He probably should mention Lancer not giving up to Rin yet, but…
This was a once-in-a-lifetime, no, a once-in-several-lifetimes chance to get rid of Gilgamesh early.
Archer summoned his bow. He brought out a fast moving and powerful Noble Phantasm.
He turned it into an arrow.
He nocked it, aimed, and let his refined senses tell him if he would hit.
He couldn't believe it.
He aimed again, just to double check.
He would hit. His refined kyuudou, clairvoyance, and Eye of the Mind senses and skills all agreed that he would inevitably hit with no possibility of missing.
No sense in wasting a golden opportunity.
Emiya released the arrow.
And gaped in disbelief as Gilgamesh brought out of his treasury, at the exact moment he released the arrow, a cart of all things.
Not a shield, not armor, but a cart.
Right in the path of his arrow.
But Emiya's aim was true.
The arrow blew through the cart, causing the vials inside to go flying high into the sky.
And some to land and then break on the now dying King of Heroes.
Archer grumbled as he watched the almost dead Archer heal and shrink.
Of course Gilgamesh had good luck, A rank if Archer knew his opponent's parameters correctly. Naturally, the King of Heroes would manage to take a certain hit and kill shot and manage to survive.
And if Archer was seeing correctly, the King of Heroes was getting younger.
Then Archer's Eye of the Mind skill started laughing at him. In Alaya's voice.
"Well, this will be fantastic," Archer grumbled as he looked around himself for whatever would cause the will of humanity to laugh at him.
Nothing to his right. Nothing to his left. Nothing in front of him. Nothing behind him. Nothing beneath him in any direction.
Archer did a spin around, examining all directions for whatever caused his skill to predict the future to start laughing. At him.
And then he looked up.
Just in time for a large splat of liquid to land on his face and in his nose and mouth.
And Archer cursed the world as he felt his Spirit Origin start to change.
Meanwhile, in a house where a boy had just tried to survive an attack by Lancer, two Servants fought an opening spar.
Saber blocked the spear strikes expertly, her lifetime of training in swordsmanship giving her skill.
And then her A rank Instinct told her to lift her sword and block a projectile.
She immediately did so, wondering if an Archer had decided to join in.
Both her and Lancer momentarily paused as her sword shattered a pair of glass vials.
Some of the liquid in the vials bounced off Arturia's wall of wind surrounding her Excalibur back at her as she inhaled in surprise from having a glass vial like one of Merlin's potions break on her sword. Some of it continued onto her opponent, whose mouth was open in a wide grin.
Cu Chulainn discovered that Protection from Arrows did not translate into protection from liquids. Which he already knew from all the time he had spent in the rain. Made for some miserable battles because he was soaked wet.
And their fight ended as both Servants started shuddering as their bodies changed along with their Spirit Origin and Noble Phantasms. Not quite so much as shrank when compared to the other Servants since they hadn't changed much since their Lily forms but changed none the less.
Their Magic Resistance did not work on one of the supreme forms of healing magic, the potion of youth.
Caster was working on a spell under moonlight, confident that her protections would keep her safe and undisturbed.
She was right.
And she was wrong.
She finished the last of her Divine Words and sighed as she looked over the protective charm she had laid on the object she was going to give to her beloved Master.
"Master Souichirou," she sighed, her new love occupying her heart.
She probably should have paid more attention to the air around her.
Because there was no malice and the thing could not kill or harm, but instead healed and restored, her defenses did not work against the flying vial.
However, the vial's cork did decide at that very moment to come out, spilling its precious contents onto a witch.
Medea's magical senses alerted her to it.
She opened her mouth to utter a word to teleport her to safety.
Only for the liquid to splatter into her mouth, bounce off the back of her throat, and down her windpipe.
And Caster's Spirit Core started to change.
Assasssin was just standing at the gate. Waiting watching.
Good thing he was so good at it. You couldn't cut down a sparrow mid-flight unless there was a sparrow near you. And most sparrows did not let a person run to them.
You had to wait for them to get close to you. Patiently wait.
Assassin did not mind.
He just wished that someone would show up and allow him to test his skills. A lifetime of training and practice only for him to finally achieve his goal-
-and discover that he was too old to test his swordsmanship against any fighter.
But he learned meditation.
And to sense when something was coming his way.
So Sasaki Kojirou struck the vial out of the air while it was still falling towards him.
But the potion itself was the Noble Phantasm, not the vial.
So the vial shattered, splattering Sasaki Kojirou with its contents.
The man blinked, his closed mouth frowning.
Then he sent a finger towards one of the splatters of liquid on his clothes. He brought the liquid to his nose where he sniffed it.
'Hmm, smells like tea.' He thought.
Then he licked the drop and tasted it.
"Tastes like herbal tea," he mused. "But I've never had this flavor before."
Then he started to change.
Berserker was the same faithful and loyal Servant he always was. Still was insane but he was Heracles, the greatest of all warriors and Berserkers.
And while his Master walked along the streets of the city, the giant stood guard over her, following her in his Astral form.
And then his senses detected something flying through the air. Some small thing, at an unlethal speed.
But it was falling towards his Master. And it might hurt her, make her suffer pain from a bump on her head.
So being the protective giant he was, he immediately materialized and smacked the item out of the air, breaking it into so many fragments and drops.
"Berserker!" Illya cried out in shock as she felt the demand to support her Servant sharply increase as he took on a more physical form.
In order to respond, the giant breathed in in preparation for his usual reassuring growl.
And found that there were some drops that had been splattered onto his lips.
And a Servant like Berserker, who could easily bellow to be heard for kilometers around, had a strong inbreath.
And so, the mad giant breathed in Gilgamesh's potion of youth.
And immediately began to shrink.
Rider was escorting her Master on another expedition to find someone to feed to her. To give her more power until they could finish the Bounded Field at the school.
"Where is everyone?" Shinji Matou demanded petulantly to the air.
Rider could understand. Tonight was suspiciously empty of everyone. No one was out. Her ears couldn't hear any sounds from anyone outside. All the sounds she could hear had the muffled timbre that comes from speaking from inside a closed structure.
"Well, why aren't you finding anyone!" Shinji demanded as he wheeled on Rider. "Do you want me to lose! You're too weak to win without eating so get out there and find someone to eat!"
Unfortunately, Rider was wearing her blindfold and couldn't see what was falling through the sky towards her at that moment. And while she was speaking, she couldn't hear the quiet sound of the liquid falling through the sky.
In other words, her D rank Luck wasn't up to resisting the fate of the potion of youth falling into her mouth.
As Medusa unintentionally swallowed the potion of youth, her Spirit Origin changed.
And an unexpected result happened to Shinji's Book of False Attendants as the Spirit Origin of the Servant it bound, changed.
"Well, this has got to be better than being adult me," Gilgamesh Lily said as he examined the upturned cart of potion of youth.
Then he looked down at himself, at his black and white casual suit.
"I think my style could be better," he said before he opened up the Gate of Babylon and stuck his head in to rummage for better clothes. "Now where is my wardrobe? And how badly did older me mess it up this time?"
"Huh," Servant Archer Lily, otherwise known as a high school student Shirou Emiya, said as he looked down at his body. "Never figured I would be on this side of the Grail War."
"Archer!" Rin, his Master, demanded across their Master-Servant link. "What happened! I felt something happen to you!"
"Well, funny you should mention that," Archer Lily said across the same link. "I think I just sniped an enemy Servant only to get caught in the oddest counterattack ever."
"Who are you?" Rin's voice, cold in suspicion, demanded of her Servant. "And what happened to my Servant!?"
"It's me, Archer," Archer Lily replied. He couldn't go by Shirou. He just saw his alternate self earlier today in school. "You may want to be sitting for this because I don't think you'll believe what I'm going to tell you."
Saber Lily blinked at the golden sword in her hand and the white dress and armor she was wearing.
"Merlin!" she yelled.
"Wait," she tilted her head cutely. "Why am I screaming out 'Merlin'?"
Then she pounded her free hand onto the back of her other hand in realization.
"Oh yeah. Because he is always the one responsible for anything weird like this," she remembered.
"Oi," Lancer Lily, the form of Cu Chulainn who had just finished training with Scathach, demanded. "Are we gonna finish our spar or not? My evil Master set limits on how much I can fight so I wanta fight as much as I can."
"Oh. Oh, sorry!" Saber Lily apologized as she finished her reminiscence on how much trouble Merlin had gotten her into. "I guess I got carried away with this development and forgot all about it."
"It's cool," Lancer Lily winked at the girl, who blushed. "This is sorta a surprise to us both, but I really want to have a good fight before I need ta retreat."
"Oh, yes," Saber Lily said as she got her blush under control. "My name is Ar- Wait! I'm supposed to keep that secret. Um, I am Saber Lily! And you are?"
"Lancer, Lancer Lily now," Lancer Lily said as he got into position to charge. "I look forward ta a good match."
"Lancer," Lancer's newer master ordered across the Master Servant bond. "Retreat."
"Ya can't be serious!" Lancer protested as he started to stand up. "I just got a good fight and you're bringing me back already!"
"Lancer, I will use a Command Seal if I have to," Kirei ordered across the bond.
"Fine, fine, stingy loser who wouldn't know a good brawl if it bit him on the arse," Lancer Lily grumbled as he turned around. "Catch ya later, Saber!"
"Ah, you too!" Saber Lily waved her now visible sword in a goodbye towards Lancer Lily. "Good-bye!"
But as Lancer bounded away, he could hear the girlish squeal as Saber Lily got a good look at her new Master.
"He's so cute! Wait, please forget I said that! Ooh, this is so embarrassing!"
Lancer Lily barked out a laugh.
Sounded like Saber would be fun to be around for this Grail War.
"Caster?" a serious adult male voice called out into the cold. "I was under the impression that this would be over by this hour. Was that incorrect?"
Kuzuki Souichirou stepped out into the courtyard and paused as he noticed that there was no woman in a dark cloak out here.
Instead there was a teenage girl, in a light and medium blue gossamer dress and a staff in her hand.
"Oh, Master!" she cried out, getting up and rushing towards him. "I'm sorry, but I think I swallowed a potion of youth!"
She suddenly stopped and tilted her head. "But that is really odd because potions of youth are really, really rare. Why would one be out here and flying through the air like that?"
"I do not understand this magus business," Kuzuki reminded the girl, who looked like a younger version of his lover. She looked much younger, like she hadn't finished puberty. "But what is the effects of this and is it reversible?"
"Um," the teenager tilted her head into a thinking pose.
Cute, was Kuzuki's first impression.
"I don't think sooo? It might be possible to grow back to my original age, but not in a timeframe of a Grail War." Caster Lily said tentatively before clapping her hands together. "Oh, and the effects are that I am a younger version of myself, with weaker skills, I can't really do offensive magecraft, but I'm still really, really good at healing magecraft. And my Noble Phantasm is Pain Breaker instead of Rule Breaker. It's really, really good at healing and can heal everything but death!"
"Oh," Caster suddenly gasped, covering her mouth as she realized something. "And I have to break up with you, Master."
The girl bowed.
"I'm sorry, and I think you are a really great man, but I am in love with Jason so I can't return your feelings," she said formally.
"Alright," Kuzuki nodded as he appeared to calmly accept their break-up. "It is illegal for a teacher to be in a romantic relationship with a child."
"But don't worry, Master!" Caster popped up brightly. "I'm going to use my new skill, Romance of the Sea Foam, to find you a good romance!"
This wasn't what he was expecting…
"Let's see, to do that, I need to examine your relationships with the women you interact with regularly," Caster Lily mused as she started to walk around, thinking about how she was going to find her favorite Master a good woman. "Ah, I need to meet your fellow teachers!"
She wheeled around on her Master, pleading with adorable puppy dog eyes. "Can I go to school, pleeeaaase?"
The former Assassin looked down at himself as he realized he was a lot younger.
"Hmm," he mused before shrugging. "Guess I should practice my swallow cutting technique some more."
So the second Saber Lily drew his sword and started swinging, practicing how to swing a sword so that a swallow could not escape.
He was going to follow his teacher's teachings. He was going to become a swordsman.
And he was going to figure out how to cut down a swallow mid-flight!
Berserker was no longer big.
Well, that is wrong. He was still big, but he was no longer a giant.
Instead he was a young man, a big and huge man.
And he is not a Berserker anymore, having been taken back to an age before his berserk rampage that caused him to undergo his Twelve Labors.
Instead, he was now a Rider. With 12 Noble Phantasms, each one relating to one of the 12 Labors.
"Wow," Illya said, as she looked over Rider Heracles's stats. "12 Noble Phantasms. The Nemean Lion, Lernaean Hydra, the Golden Hind, Erymanthian Boar, the Augean Stables, the Stymphalian Birds, the Cretan Bull, the Mares of Diomedes, the Girdle of Hippolyta, Geryon's cattle, the Golden Apples of the Hesperides, and the Cerebus of Hades."
She looked up at Heracles who smugly smiled.
"And you can summon all of them!" she squealed. "Which one should we use first? I want to see the cerebus!"
"All right, little Master," Heracles Lily chuckled as he flexed his muscles under his Master's admiring gaze before extending his palm down to the level of her knees. "But I don't think this street is big enough for it. Climb up and I'll take you to a place where you can see it."
"All right!" Illya cheered as she jumped onto the hand which brought her up to his shoulder, where climbed on, settling in for Berserker travel. "Let's go!"
"As you wish, little Master," Rider Lily chuckled before using his A level agility to run off towards the forest.
Within a minute, the duo was safely hidden among the trees.
"Cerebus, Cerebus, Cerebus," Illya was cheering enthusiastically on the tree branch that Heracles had dropped her onto.
"And here you go!" Heracles roared "The Twelfth Labor, Capturing the Cerebus!"
Illya cheered again as a massive, black furred, three-headed dog appeared in the clearing before her.
And then screamed as it lunged at Heracles, all three heads snarling.
"A feisty fellow isn't he!" Heracles yelled as he started to wrestle the giant dog. "Give me an hour and I'll have him under control!"
"What!" Illya yelled as she started to read the details for Heracles's new Noble Phantasms.
"Oh," she said as she read the fine print. "That… actually makes sense."
Heracles Lily has yet to undergo the 12 Labors. The task to accomplish each labor must be accomplished before the Noble Phantasm will obey the Servant or before Heracles Lily will be able to use the product of such a battle. Each of the 12 Labors can be carried out in the modern day but requires the approval of the Master before each can be started. The Master takes on the role of Eurystheus but can only choose the 12 Labors as worthy feats for Heracles Lily.
"So he has doing 12 Labors as his Noble Phantasm," Illya sighed before brightening up. "Then that means that I can watch him do each! And he has to bring the rewards to me! Go Berserker! I mean, go Rider!"
"Thank you Master!" Heracles yelled as he punched one head of the dog into a nearby tree, causing the old and wide tree to topple over.
"Too bad, he lost Godhand," Illya commented as she swung her legs while sitting on the tree branch, watching the fight unfold in front of her.
The former Rider Servant petrified Shinji with her eyes as he had started screaming at her younger form and was annoying her.
"As my older sisters would say, 'Who let the howler monkey in? Go chase it away!'" Medusa Lily said whirling her scythe.
Medusa Lily, like Heracles, had also experienced a class change. Into Lancer.
And she was now a young girl, the same apparent age, weight and size as her older sisters.
"At least I am cute now," the young goddess said as she twisted and turned, examining herself next to the stone statue of her annoying former temporary Master. "I would hate to still be ugly like my older self."
The girl finished her examination of her armored dress and nodded.
"Alright, time to return to my Master," the girl decided, vanishing Harpe and jumping off into the night sky, following the trail of her mana source back to Sakura Matou.
The remnants of the Book of False Attendants laid petrified in the now stone Shinji's pocket. The book had been binding on Rider Medusa, but not Lancer Medusa Lily.