Defining Their Relationship (Fate/stay night)

/N: Defining Their Relationship was a P atreon Poll Winner originally written in 2018 and posted to HF in 2021. Posting it up here and now for people to enjoy!

Themes: F/F, Rough Sex, Dom/Sub, Anal

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Rin Tohsaka woke up with a gag in her mouth, a blindfold over her eyes, and silk cloth restraining her wrists behind her back. This shouldn't have been possible, for a number of reasons. For one, she wasn't that deep of a sleeper. For two, how had anyone managed to get past her home's defenses without at the very least alerting her to their presence. For three, even if those first two things meant nothing, surely the Saber she'd summoned just the day before should have been able to protect her while she slept!

Of course, all three of these reasons were rendered null and void by the simple fact of just who it was that had trussed her up in her own bed, rendering her helpless. Within minutes of Rin awaking, she feels hands on her, and a familiar voice fills her ears.

"Ah, there you are Master. Finally awake."

Rin's eyes widen a moment before the blindfold is torn from her face, causing her to blink them rapidly as she readjusts to being able to see again. Eventually, she makes out the face of her servant, of Saber leaning over her. Mordred, because that's who she managed to summon, smiles down at her wickedly.

"Don't need that pesky thing anymore, do we?"

Growling through her gag, Rin struggles a bit. Just what did her Servant think she was doing? If Rin had use of her voice, she would most definitely use one of her Command Seals to bring her unruly Servant to heel right now! Mordred might have been known as the Knight of Treachery, but that didn't mean she got to betray RIN!

"I enjoy that look in your eye, Master. Before we continue, I suppose I should explain myself, shouldn't I? Obviously, the gag is to keep you from using those pesky command seals on me. No point in wasting them putting a stop to this… not when we both know you want it?"

That last bit is said almost breathlessly as the half-naked Mordred leans forward, her lithe body almost completely on top of Rin's, her face inches from Rin's face. Want it? W-Want what?! Rin is left wide-eyes and confused, even as Mordred continues on with that same smile.

"You were quite arrogant yesterday; don't you think Master? Commanding me about, ordering me to remove my armor so you could ascertain my identity… looking down upon me solely for my size and my past. You really stoked the flames quite a bit, you know. I wonder if you meant to, or if you simply couldn't help yourself."

What was Mordred talking about? Certainly, all of that had happened like she said. But that was Rin's right as a Master. In the end, Mordred was her Servant and Rin was in charge here, damn it all! Glaring up at the blonde, the female magus does her best to convey this through her muffled voice. Not that it seemed to have much effect on the Saber-class Servant. Grinning all the wider, Mordred reaches out and squeezes Rin's cheeks between her fingers.

"For a knight such as myself, no matter the challenge, be it horse or woman… the harder they are to handle, the greater the satisfaction that comes from taming them. And you have made yourself quite the appealing conquest, dear Master."

What was Mordred going on about?! Wha- Rin's eyes go wider still, nearly popping out of her head when her Servant abruptly stuffs a hand down her pants and panties, pushing her fingers right up against Rin's cunt. An involuntary moan escapes from around Rin's gag, even as Mordred grins ferally at finding her Master just a bit… wet down there.

It wasn't Rin's fault. Sure, she was a little aroused, but that was a simple byproduct of being tied up. It wasn't like she was willing to give up all control just because she had a small bondage kink! Of course, now that Mordred was finally making her own desires abundantly clear and Rin was in turn beginning to realize that this wasn't some sort of true betrayal with her life on the line, it was becoming harder and harder to ignore how good the silk cloth felt around her wrists, or how satisfying it was to sink her teeth into her gag.

"Do not worry, darling Master. I will fight this war for you and for myself. Together, we will take on all competitors and win the day. But before then, we both need to be on the same page. We need to know where we stand… and where we kneel."

Mordred's smile is wicked and seductive as Rin's eyes go crossed from the blonde Saber slipping two slender fingers up into her Master's cunt. The indisposed magus can't do much beyond moan helplessly as Mordred works her digits in and out of her.

"Don't give in too easily now Master, or I might just think you a slut."

Of course, those teasing words cut through the haze threatening to fall over Rin's thoughts better than anything else could. As Mordred smirks down at her, Rin snarls through her gag, growling as she once again struggles against her bindings. Though… perhaps not as hard as before. Mordred just laughs in response and continues to slide her fingers in and out of Rin's body, even as it bucks up and down beneath her, trying in vain to throw the other woman off.

But Rin is just a baseline human magus, and Mordred is a Heroic Spirit, brought forth by the Holy Grail War to fight for Rin. Needless to say, one of them is much stronger than the other. Its not Rin, not by a long shot. And perhaps that doesn't just go for physical aptitude, but also mental. Because as Mordred fingers her cunt, as Rin fights back as best she can, the pleasure is still building within the naughty, kinky magus.

Eventually, Rin moans and bucks her hips in an entirely different way as her pussy juices squirt out of her, coating Mordred's hand and fingers entirely. In response, the blonde Saber coos at Rin, pulling her hand free of the magus' cunt and bringing her fingers up to Rin's mouth. She shoves the messy digits right past Rin's gag, and Rin instinctively begins to lick and slurp at the intrusion, even as she gags a little.

"That's good… that's very good, Master. You're gonna be my good girl from now on, aren't you? My sexy little prana battery."

To be so debased, to be so degenerated… it should have infuriated Rin, given the outward face she put on to everyone else. It certainly humiliated her… but it also aroused her beyond all else, and her hips buck again at Mordred's words, causing the Servant to grin wickedly. Mordred hooks her fingers into Rin's gag and all but tears it out, allowing Rin to work her jaw back and forth a bit, allowing her to speak, finally.

And all without getting any sort of concession from her. But then, Mordred seems to know this as she sits back for a moment and smiles down at her Master.

"Well? Now's your chance, Master. All you have to do is waste one of those three valuable commands on bringing me to heel."

For a moment, there's silence. Ultimately though, Rin turns her head to the side, blushing deeply as she answers her Servant.

"… I won't."

Chuckling darkly, Mordred reaches out and grabs Rin by the hair, forcing her to look back at her.

"I knew that already, now didn't I?"

Pulling Rin along, Mordred sits back on her Master's bed, dragging Rin up off of her back and onto her knees. Not her hands though, those were still bound behind Rin's back, making it all the easier for Saber to drag Rin's face all the way down to her crotch. Letting her clothing fade away, the Knight of Treachery reveals her own dripping pussy lips to her Master, smirking wickedly down at the magus as she guides Rin into place.

"Then get to work putting that mouth to better use, Master. You can start here."

Rin's gaze flicks between Mordred's smirking face and the blonde's cunt a couple times, but in the end the bound magus leans forward the rest of the way and does as she's told, allowing Mordred to grind her face into her cunt as her tongue slips from betwixt her lips and begins to eat Mordred out. Groaning, the blonde Saber grips hard at her Master's hair, even as she humps up into the young woman's face.

"Just like that, Master~ Just like that!"

With a wide grin, Mordred tilts her head back as she lets Rin get to work. Dominating and subjugating the arrogant magus gave her no end of satisfaction, but having Rin willingly eat her out was even better. Wrapping one leg around Rin's head, Mordred lets out a sigh, leaning back for a moment as she just enjoys the young woman's tongue.

However, the more she sits back and lets Rin do all the work, the more she finds her gaze zeroing in not on her darling Master's head, but on the female magus' squirming ass. In her current position, Rin's behind is jutting up into the air quite spectacularly, wiggling there because there's not much Rin can do in her current position, with her face buried in Mordred's crotch and her arms tied behind her back.

The more Mordred stares, the more she wants it. Eventually, the slim blonde Saber leans forward, folding her body over Rin's while reaching out with her free hand to grab the back of the magus' pants. A simple sharp tug with her enhanced strength sees the backside of Rin's garments torn from her body, exposing a pair of cute red panties and her bubble butt.

It also provokes a muffled squeal from Rin, but Mordred just giggles as her Master struggles a bit at the sudden aggression.

"Calm down, Master. I'm just making sure you have as much fun as I have~"

Of course, Mordred is a pretty short woman herself. She's not quite tall enough to reach all the way over Rin's ass in order to properly finger the girl's cunt from her current position, and she's not willing to change things up just for Rin's benefit. She's still quite enjoying the female magus' tongue, after all. Instead, the blonde Saber settles for her Master's ass, pushing aside Rin's panties and sliding a finger down the girl's ass-crack, before eventually pushing up against Rin's sphincter.

As she slowly worms her way into her Master's back door, Mordred gets quite the pleasant surprise. Rin almost immediately begins to writhe and wiggle in a whole new fashion as Mordred feels reverberating moans through her cunt, the magus exceptionally weak to anal from the looks of things. Cooing over this discovery, Mordred snickers, even as she works her index finger in and out of Rin's bum.

"Mm, Master… it looks like I've found a weak spot. Are you enjoying this, Master? You certainly sound like you are."

And Rin is, as much as she hates to admit it. She didn't even know. Unlike the bondage fetish, which she's really tried her best to suppress, Rin had no way of knowing that having a finger inserted into her anus would cause this sort of reaction in her. But here they both were. Her moaning into Mordred's cunt and writhing her tongue about, and Mordred sliding her finger in and out, pushing it this way and that around inside of Rin's ass.

Its no wonder that she quickly cums from the anal intrusion, though she does her best to get Mordred off first. But in the end, she fails. Only by a little bit, as her squealing and cries of pleasure from the anal fingering Mordred is visiting upon her helpless behind end up bringing the blonde Saber over the edge as well.

Grunting, Mordred's body bucks as she squirts her own pussy juices all over Rin's face. Her sexual fluids flow down the female magus' chin and along her neck, even as Rin swallows what she can. Its actually quite sweet and tasty, Mordred's discharge. She finds herself drinking it down, right up until Mordred finally pulls back and drags Rin up from her crotch.

Their lips crash against one another as the Heroic Spirit dominates Rin's mouth with a deep, tongue-filled kiss. For the first time in a long time, Rin Tohsaka finds herself completely relaxing, simply melting into her Servant's embrace. Saber might be caustic and aggressive and altogether domineering, but Rin… somehow, Rin feels safe with her. When Mordred says she'll help Rin fight the war and defeat her enemies, the female magus believes her.

As they continue to kiss, Mordred reaches behind Rin and unbinds her wrists, drawing the young woman's arms back around herself and holding her hands tightly. Then, she draws back, giving Rin quite the wicked smile as she looks down into her eyes.

"I think this is the start of a beautiful relationship, Master."

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