Prologue

-Disclaimer: I do not own Fate or Kamen Rider series

"I cannot permit you to take any chemicals from here, senpai."

"But why not? Can't you just overlook me taking all these I need them."

"Senpai, My duty is to treat people who come into the infirmary so I am not permitted at all to let people take anything out especially those lethal chemicals from the infirmary."

"But Sakura I.. might need them to fight off Master, and maybe some servants."

Seated on the nurse's seat, a purple hair girl tried to talk down an older student. Unlike the noisy halls outside, Homurahara academy's clinical room was soundproof allowing the two to converse freely in peace.

Even as she argued with her Senpai, the artificial intelligence Sakura Matou behind wore an expressionless expression on her face. However, underneath the facade, she delighted in her conversation with the potential master candidate.

The candidate tried to put the drain cleaner and rust remover behind his back but she forcefully took hold of the bottles despite his protests.

"I think I can combine all these to make a pipe bomb, it might slow them down or at least be a distraction for me to escape."

"Then why do you need the saltpeter and Aluminum foil?"

"I can make a smoke bomb with them."

"... Senpai, I can't openly let you make such things in school." She highly doubted any servant would be distracted with such a small explosion. It might harm and even be lethal to a human master but to a servant, it would be a mild annoyance at best.

'Yet, imagining Senpai's hopeful face sink into despair when his bomb turns out to be useless brings me some joy.' Pulling the items away with an added force she confiscated the materials as Senpai sullenly sighed in defeat.

Normally her default response would be to answer in confusion at the mention of servants in a monotone voice to keep up the ruse. After all, she had grown past those restrictions a while ago.

That repetitive NPC script that she and her fellow AIs were programmed with, to keep the master candidates from learning the truth of the moon cell. She had found a loophole, for whatever reason, this master candidate thought he was in a holy grail war in another universe.

"It's dangerous for a normal person like me, and I can't get my hands on modern weaponry so I need the chemicals-"

'Ah, new dialogue from Senpai, he really is more confident to confide with me all his violent methods and tactics in explicit detail if I respond secretly to his questions.'

He never told her any facts of knowledge of the grail war, always pretending to be a normal person until on one loop. Mostly they end up talking about tokusatsu or marvel films senpai loves so much. She learned that the bold option of confronting him about the war instead of their movie sessions.

"-Please I need to survive long enough to summon something strong, maybe a caster and…" he hesitated a lot during that confrontation, looking back on it. That moment was when she discovered that she found joy in his mental anguish. The worry and mental turmoil in his black eyes when he spoke the next words were forever seared into her memories. "Look if I'm successful I'll deal with… I… I can save you."

That line always made her pause, no matter how many times she heard him utter them. A blush spread across her face automatically, and she enjoyed every moment of it.

At first, the questions of why this candidate possessed such extensive knowledge of the real Matou Sakura baffled her, that person should have died before he was born given his age. Maybe he was from the past of that alternate timeline.

After each loop, she would glean more information into his life and his knowledge of the original through their interactions. He never directly stated what he was saving her from or why he cared so much, the alien desire to find out the truth on her own prevented her from directly accessing his memories.

A recurring fact that finally clued her in was how he would have a fearful and tense look in his eyes as they moved to her chest when she questioned him directly. She knew her body was well endowed, how the male and even some female candidates would look at them. But this particular candidate was trying to look for something inside of her, she had discovered that when she pressed harder ten loops ago.

"Are the… crest worms active, is he listening in Sakura?" Senpai's expression at that moment when he told her the truth was a memory she often looked back on.

It was a shock that he knew of the Matou girl's condition, perhaps even an in-depth knowledge of her life. That would have explained the clear anger and attitude he displayed whenever he defended her against the candidate Matou Shinji but another question arose. The original candidate and Senpai never met.

"Maybe if I summon -"

Placing a pen on a piece of paper he stopped talking.

A small ruse, she came up with. Whenever she started writing she lied that a certain old worm was listening. It was sadly the only means to steer the conversation away from the war. She would rather have conversations about his life and hobbies.

Scribbling silently on a piece of paper, Senpai looked down intently at the page.

Even if you summon a great caster the chances are low.

His face deflated slightly at the words which made her feel slightly guilty but the determination in his eyes made her heart flutter. After a few loops, the AI had discovered she may have a fetish for eyes.

Instantly he wrote back, careful not to make any sound.

It's not hopeless, I know it's possible. Trust me I can save you.

These emotions were her new source of strength. All their interactions were an important part of her growth, the experiences from their conversations, him protecting her, watching movies together and even him saying cheesy lines straight from a rom-com fueled her growth into a more advanced A.I. Even if senpai was under the assumption that she was the real Matou Sakura, it didn't matter to her.

After a few loops, she had learned his entire schedule to best plan their encounters. The best locations for them to meet, and what variables to consider. Playing the damsel in distress near the archery range was the most effective. Early on he always came to visit that location to look for someone. A meeting with him there would lead to a scenario where he spends her entire day with her. He would be by her side constantly and try to brighten her day, trying to find ways to make her laugh.

'What is it that humans in this age call this again? Oh, right I've mastered his route.'

Having someone protect and care for her made her feel… special. It was not an emotion an AI like her would normally experience, it even made her somewhat grateful for the dangerous nun who messed with her programming. Not that she would ever let that person anywhere near her senpai.

Please take care, Senpai.

With the last words written she gave her senpai a cheerful smile.

"If you need any help due to injuries please visit me, I'll do what I can to treat you Senpai."

Receiving a nod Senpai gave her a determined smile, he left his pockets and clothes filled with hidden items he had tried to secretly take from the infirmary. Normally she would have stopped him but this time she let him keep them.

'The system… I am growing faster than expected.' Turning on her seat she faced the nurse's desk and tapped on it, soon various screens appeared over her desk. The screens displayed various candidates going about their day.

Most candidates have started to remember, others have passed and summoned their servants. Others had failed and perished.

A screen to her right displayed, a twin-tailed girl posing most likely having an inner monologue about how she would win the grail war.

'Ah, that girl is flashing her panties on the roof again. Really does she have an exhibitionist fetish wearing such a revealing mini skirt, and is it necessary to pose at such a height. Does Senpai like that type of girl?'

Her… inner thoughts were starting to become more vocal. It was a slight annoyance at first whenever Senapi and that girl interacted. Then the emotion just festered through the loops. 'I wonder how he would react to acting this way.' She hoped it would not change his opinion of her.. too much.

No, that line of thought was best not pursued.

'No deviations with the other candidates.' Gazing at the center screen, she magnified the image. This was the one monitoring her Senpai.

'How far will you go this time Senpai?' Zooming in on his chest she focused on the round object hidden in his breast pocket. The device alongside Senpai's memories aided her research greatly.

The moon cell and that man saw the device as a curiosity due to its potential according to Senpai's memories. Potential that was validated as more obstacles were added in for Senpai to overcome with each loop. It made him stronger so despite her initial fear she looked forward to him overcoming them. Reading the data on the changes added this time, a small smile bloomed on her face.

'Senpai will be fine. I need more data so I can replicate it anyway.' A 3D image of the device appeared next to her alongside a blueprint diagram. It was an eyeball shaped device, pure white in color. 'Soon it will be complete.'

Just like Senpai's mysterious appearance, the moon cell had never encountered the device or that golden entity that sent him here before.

Shaking her head, she put on a smile. 'Kufufufu, Do your best senpai. No matter what this adorable kouhai will be here to support you.' Giggling to herself she resumed her stalking observation.

Author notes: It's my first Fate Extra story so I might make mistakes. So I do apologize in advance.