No spoilers. This kinda just popped up out of nowhere so here ya go.
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In holy grail wars, servants are meant to kill one another or even the masters of other servants. Those who have cruel or thorough masters can sometimes aim to take the lives of both the enemy servant and master. However, there is also the chance that two masters may form an alliance and temporarily work together to take down all other competition. It would be this latter case that (y/n) found himself in. As a servant, a distant hero of the past, he found himself summoned to this grail war and working together with a Saber who absolutely despised him.

This seemingly foolish root of hatred began when (y/n) was ordered by his master to save Saber from Berserker's onslaught. Despite the saber class supposedly being the strongest of the seven classes, Berserker had been close to winning that fight simply because Saber's master was not strong at all. The poor girl was only dragged into the war by default, or so it had seemed at the time.

Saber had held it against him ever since then for saving her, which (y/n) found to be very strange. Usually one would convey gratitude to their rescuer. Regardless of how much Saber hated him, (y/n) himself could not even think to dislike her in any way. She was a woman of great honor whether she admitted so or not. It was for this reason, among others, that he would often find himself silently admiring her. If he were to ever speak a word of praise anywhere near her, he held no doubt that she'd try to fight him.

During the past four months of the drawn out war, he'd often find himself fighting alongside her. When their battles ended in victory, she would offer him a fist bump, which he quickly accepted. Accompanied by it would always be a bright grin as she bathed in the triumph of winning. Then, she would remember once more that she hated him, and that grin of hers quickly turned into a glare followed by the withdrawal of her hand.

(Y/n) especially liked when he would get slightly injured in a fight. The injury itself was always distasteful, but Saber would never leave his side at those times. There would often be constant inquiry about whether or not he was okay until Mordred was able to see for herself that he was healed and back to normal. Then, she'd act as though none of it took place and go back to hating him. Although she was often rude to him, Saber's rare displays of kindness or acceptance still lingered and became the basis of (y/n)'s view of her.

That's why when the end of the war drew near, he began to worry. His wish for the grail was not worth throwing away his victory, but he did not want to harm Saber in order to reach that goal. With only one other servant remaining, they could end up fighting each other at any time. It was Saber herself who brought up such topic when they were by themselves. Their masters had gone to investigate a matter regarding the final servant against them, and Saber's master had insisted that they leave their servants behind. Of course, both (y/n) and Saber had been against the idea, but in the end, they obeyed their given orders.

"Aren't you worried about having to fight me?" Mordred spoke without looking up from her food. Both wore casual attire and sat across from each other sharing a meal that neither of them truly needed. (Y/n) gave a slight laugh at such irony. "What are you laughing for? I'm serious," Saber growled.

"Ah, sorry. I was just thinking about the same thing. Is it my safety that worries you or is it your own wellbeing that you're concerned about?" he said. Saber looked as if she wanted to reach across the table and strangle him right then and there.

"I'm not worried about anything at all! You're the one that's going to have to worry," she snapped. "But I'm serious. Doesn't it bother you that we still have to fight. We've been allies this whole time and now we're expected to just fight to the death? Your master might hesitate, but I know for sure that mine won't even think twice about breaking this alliance the moment things are narrowed down to just us." Saber pointed at him with a glare. "And you look like you're okay with it too! Why are you always so calm? It's annoying!" she added.

(Y/n) gave a slight smile which only seemed to anger Saber even more. "I'm not necessarily calm. I guess, from your perspective, it may seem that way. I'm just trying not to upset you, yet no matter what I do, you always end up mad at me in the end."

Saber was about to say something to him, but she didn't seem like she could even find the words to say. "Shut up! You don't know what you're talking about," she suddenly snapped.

"I don't get why you hate me so much, but it's quite the opposite with me. I wouldn't even dare bring myself to harm you even if you were trying to kill me. You're just an amazing servant. No, you're a truly unique knight. If I knew what your true name was, I'd call it often," (y/n) confessed. There was no reason that he shouldn't let Saber know how he felt about her. They could very well be enemies the moment their masters returned. If he were to leave this world, his memories would disappear with it, so why not take this chance?

Saber was dead silent. Her stare held no form of hatred, but (y/n) was also unsure of whether she had accepted his words. "The hell did you just say...?" she mumbled in disbelief.

"I-" (y/n) was silenced before he could say anything else.

"You're not fair at all! Why would you go and say something like that? I asked you that so you could give me a reason to regret killing you!" Mordred seethed.

"I thought you'd be quite happy to take off my head. Not that I'd let you..." (y/n) muttered.

"I don't hate you! Why would you think something like that? If I hated you, I'd have killed you long ago." Saber facepalmed and kept her gaze anywhere but on him. "I'm...not supposed to tell you my real name," she said. (Y/n) almost couldn't hear her. He was mainly focused on the fact that she truly did not despise him as much as he thought she did. "When this all over, I'll trust you enough to tell you what it is. And I'll make you one of my knights," Saber declared.

"Your knight? Why? Are you a king back where you're from?" (y/n) asked, hoping to get some sort of clue to Saber's identity.

"No, but I should have been. I was worthy, father just didn't acknowledge it. But now I'll win this stupid war and become king!" Mordred answered without even realizing (y/n)'s intentions.

"So you were a prince. Interesting," (y/n) mused. Saber had made it clear through a few unfortunate encounters with other servants that she did not like being compared to or pointed out to be a woman. (Y/n) was careful to keep such in mind, and it paid off even now as a slight smile began to form on her face.

"Heh, you really think someone like me was a prince? No way. I'm clearly a knight. You're just trying to figure out what my name is," she said. He wanted to speak to her more and ask her many other things that he had wondered all this time, but he knew that it wouldn't last long. "What's with you all of a sudden? Why are you looking at me like that?" Saber wondered.

"Can you do me a favor?" he asked instead of answering her. She hesitated for a moment but gave a quick nod so he would continue. "Close your eyes for a moment. I promise I won't do anything unruly."
Saber was suspicious of his intentions, but their trust was strong with one another. She did just as he requested without even complaining. (Y/n) wasted no time in materializing his second noble phantasm, a necklace of divine protection. He leaned across the table and hooked it around Saber's neck. She opened her eyes causing him to freeze when her gaze met his. Before he could back away, she reached up to take hold of his face.

"You idiot, don't you need this?" she muttered, staring at him calmly and plainly. He'd have kept staring back for eternity if she hadn't spoken.

(Y/n) couldn't help but laugh at her. "I have no use for it. You wouldn't harm me."

"You annoy me so much," Saber sadly stated. "Don't blame me if anything happens to this stupid necklace." She let him go, and he returned to his side of the table wondering why he hadn't used the opportunity. "And wipe that stupid smirk of your face!" she complained.

"I'm not smirking," (y/n) innocently claimed.

"Then stop whatever it is that you're doing," she snapped.

"What, looking at how admirable you are? Can I not do that?" Now he was definitely smirking as Saber fumed in both embarrassment and rage. All (y/n) did was watch with his face proped against his hand.

"I'm seriously going to kill you! Just you wait!" Saber mumbled.

"Before you do, I'd at least like to do the right thing and take you out somewhere," (y/n) said. He was expecting Saber to fuss at him in retaliation, but she fell silent and looked at him. He thought for a moment that expressing that thought was a mistake until she actually said something.

"Yeah...that would be cool," she spoke. Her gaze quickly left him as a slight smile nearly formed on her face. It was her subtle lingering moments like this that led him to pave them a future where no one had to die and the war could still be won.
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Alright, I'm behind schedule which isn't good. I've got to finish these last few oneshots quickly. Until then you epic readers!