Side Story: Mana Tranfer w/you, Rider, and Rin

The absurdity of the situation was almost enough to keep you from being able to perform at all. Almost. Lying side-by-side with Shirou Emiya on a massive bed, the two of you shirtless and waiting, felt like a bizarre dream. The reason—a sudden, critical shortage of magical energy requiring an immediate, large-scale transfer—was a distant, clinical thought in the back of your mind.

It was the Holy Grail War. Somehow, you ended up summoning a sultry Rider Servant. Big boobs, lady-like yet seductive, and often wearing a blindfold. She was the kind of woman that, when summoned by a good master like you, smiled and showed her softer side.

Rin Tohsaka and Shirou were not masters in this Holy Grail War. They were only here to aid you, an innocent. An innocent with a Servant, yes, but let's just say it wasn't exactly an intentional summoning...

But that was neither here nor there. What led to these circumstances, only that they were your circumstances. Rider was not merely struggling with mana, her Spirit Core had been damaged. It needed to repair, or else even using her Noble Phantasm would be impossible. With Rin, Shirou, and yourself, there was a glimmer of hope for repair.

The immediate, pounding reality was Rider and Rin Tohsaka standing at the foot of the bed.

Rin looked like she’d rather be anywhere else, her arms crossed tightly over her chest, a faint blush high on her cheeks. “This is purely a necessary procedure,” she stated, her voice tighter than usual. “A calculated mana replenishment. Nothing more. S-so don't get the wrong idea, you two!"

Shirou laughed, sweat-dropping. "Obviously, Tohsaka." His eyes did wander and you did the same. Rin's classic black skirt was on, though not her red top. That was discarded and she was only in a thin white top.

Cocks stirred. Balls churned.

"All we have to do is give you enough mana, Rin," said Shirou. "Enough to jumpstart that spell of yours."

"I-I would have been able to do this if I didn't already use my jewels," Rin grumbled. "But now..."

To make it simple, Rin being the genius she was had a spell that could repair Rider's Spirit Core. Such a spell normally required ten mana-soaked jewels, which she currently didn't have. Which meant she had to use you and Shirou as mana batteries. She was going to have to supercharge herself and swallow or take at least three loads.

And the thing was...Rider had to do the same. Less so because of the spell and more because of the damage itself. A damaged Spirit Core was like having a leak. Every second was causing her to weaken.

Rider certainly did not look weak though. She was in her usual erotic black dress, arms to her aside, the only missing piece being the boots. Her long pink hair sat over her butt and she had no issues with being a statue of cool, predatory, sexy calm. A knowing smile played on her lips, her violet eyes hidden behind her usual blindfold, though you had no doubt she could see everything. Everything.

“Relax, Tohsaka,” Rider said, her voice a low hum that vibrated straight through your boxers. “We shouldn't make the men nervous~"

"R-right..."

Rin swallowed. From what you understood from Shirou, she and Rin were dating but hadn't gone very far in terms of sex. Only kisses and the ever so often handjob. Never sex. This would be their first.

So it was only fair for Rin to crawl to Shirou with the grim determination of a soldier marching into battle. Boyfriend and girlfriend. Shirou tried to comfort her with a grin. It was hard to tell whether it settled the tsundere's nerves.

Rider, however, flowed up the bed toward you. She was so liquid and graceful the mattress barely dipped. Boobs stole your attention. That dress of hers, with how tight it was and how it pushed her tits up, was a damn male gaze stealer. Even Shirou's eyes flicked away from his girlfriend to the crawling snake.

Smirking, Rider put her face above your boxers. A long, pink appendage that was far too long to be an ordinary tongue slipped out to tease you. But it was her tongue. This was not a human, this was a monster. A woman that was of divinity as well as hate itself.

Yet here she was, teasing your cock through your boxers. Near your bulge, she was a wall of soothing lavender scent and immense softness, her long, luxurious purple hair spilling over your chest like a silken veil.

“Now,” Rider murmured, her voice a private secret for your ears alone. “Let’s see what we’re working with.” Her cool, delicate fingers hooked into the waistband of your boxers. On the other side of the bed, Rin was performing the same action with considerably less grace, fumbling slightly before tugging Shirou’s boxers down.

The cool air of the room hit your exposed flesh. And there they were. Two flaccid cocks, side-by-side by circumstance. Both were…