Coupling Practice
“Hngh...”
Karen's back arched softly. At the same time, her thighs spread straight out in a line, her toes wiggling at the tips.
Flexible body.
Her legs splitting so naturally showed she never slacked on training. And surprisingly, not a bit of excess fat anywhere. It had already been an hour of helping Karen with her prep exercises. Someone might think it was overkill for something like stretching, but it was actually crucial. This yoga or Pilates-like routine helped smoothly activate the mana nerve system built inside a female pilot's body.
“You can let go of my hands now.”
Karen spoke up after a long stretch. Looked like they were done. Regretfully, Netoru released his grip as she asked. He'd been holding her hands the whole time, so her warmth lingered vividly in his palms.
“Mm... Let's wrap up the prep here. You must've been bored out of your mind waiting. Right?”
He'd never once felt bored. Honestly, watching Karen was plenty entertaining. There was something endlessly appealing about a woman sweating through her workout. Especially the way her cleavage peeked out every time she bent forward through that tight tank top, or how the sweat-soaked fabric created this tantalizing mix of light and dark shades in perfect balance—it was downright stimulating.
“Gonna grab some water real quick.”
Karen wiped her sweat with a towel, spotted the water bottle on the table, and stood. Netoru turned toward the faint whispers of the twin sisters nearby.
“Haa... R-Ran... Don't shake your hips like that all of a sudden...”
“Hehe... Sis! This is training too, training!”
“B-But... Netoru's right there...”
They weren't trying to flaunt their secret relationship, were they? Or did they think their voices wouldn't carry? As he glanced over curiously, Netoru suddenly locked eyes with Ran.
“Hii!?”
“Kyaa? W-What, what's wrong!?”
Ran's reaction was explosive, like she'd been caught red-handed in something embarrassing. She clearly hadn't expected eye contact and jolted in surprise.
“Th-That...”
Her face flushed red as she averted her gaze. Rin stared at her oddly for a moment, tilting her head, then seemed to catch on and shot Netoru a glare.
“Why you sneaking peeks like that? You're embarrassing my sis. Get rid of that dirty stare already.”
Netoru just let out a hollow chuckle at Rin's bratty tone. In that instant, a flash of the twins' secret indulgence in the corner of the base crossed his mind—hidden from prying eyes.
...Does this count as incest?
Either way, one thing was clear: it wasn't something that'd earn them good looks from anyone. Ever since he'd learned about it, Netoru hadn't been able to see the sisters the same way. The shock had been that intense.
“What? That look on your face.”
“Nah, nothing. Just nice seeing sisters get along so well.”
“...What?”
Rin scrunched up her face, clearly unsure how to take that. But she didn't seem to suspect he'd caught on to her secret with Ran, so she just turned away with a huff.
“Sis. Let's get back to it.”
“Mm... Okay.”
Ran nodded and straightened her posture. She was straddling Rin's waist right then, their hands linked and fingers interlocked—like she was riding cowgirl. That was the coupling practice method. It mimicked the coupling state without boarding a Holy Knight, purely for training.
Just then, Karen slipped back in after her water break.
“Alright, our turn for coupling practice.”
Netoru nodded and slowly lay down on the mat she'd been sweating all over just moments ago.
Or at least, he tried to. Karen, who'd been watching, flinched and stopped him.
“W-Wait a sec...! Hey! You weren't gonna lie down there, were you?”
“Why? What's the problem?”
“Are you nuts? No way! I brought a fresh mat—lie down here.”
“Hm. I like this one.”
“......You serious?”
Karen's gaze turned icy. Like the temperature had dropped a notch from her usual stare.
“Of course it's a joke.”
If she didn't like it, no helping it. Netoru lay down on the new mat she'd brought. All that was left was waiting for her to climb on top. As he waited with a twinge of anticipation, he saw Karen inching closer on all fours, cautious as ever. Her feet planted on either side of his waist, and she froze there.
Their eyes met in that position. But Karen was the first to look away, sliding her gaze aside.
“......Mm.”
Embarrassment was plain on her face. Well, it was only natural. Even if it was training, the pose was what it was.
“Don't worry. I won't complain even if you're heavy.”
“...Who said I'm heavy?”
Good, the joke landed. She grumbled a bit, then slowly lowered her hips until her ass settled demurely onto his stomach.
Mm.
The moment her soft flesh made contact, a pleasant weight spread through him. Squishy and warm—it stirred an urge to grab right then and there. And with those leggings on, her body heat and skin texture came through even clearer.
But he held back. Instead, he watched as she twisted a little to get her posture right. Once she was set, she extended her hand with a silent look that said grab it.
Netoru reached out in response, taking her hand and interlocking their fingers tight so they wouldn't slip.
Karen trembled slightly, like she was surprised. She blinked for a moment, hesitating, then murmured tentatively.
“Netoru. You don't have to grip that hard...”
“Nah, this is better for forming the mana path.”
“...Huh? Really?”
Innocently, she tilted her head. Sorry, but it was a lie. He just wanted to hold on tight.
“Anyway, I'll guide the mana path formation, so you just stay still. Don't move a muscle.”
She still looked puzzled, but she closed her eyes and gripped their interlocked hands harder. Focusing her mind, she began awakening the mana nerve system inside her.
Linking hands like this wasn't just for balance. It was to form the mana path connecting their mana nerve systems. In the cockpit, the Holy Knight's controls handled that automatically during coupling. But for coupling practice, they had to create it artificially by linking their bodies this way.
Truth be told, hands weren't even necessary as long as they connected somehow. Objectively speaking, linking hands to form a mana path was pretty inefficient. If emotions aligned and contraception was handled, the most reliable way was straight-up sex. Why bother linking externally when you could connect body to body?
Of course, saying that to Karen's face would earn him a slap. Still, who would've thought he'd end up doing coupling practice with her? It was meant for partners whose coupling wavelengths matched.
Netoru and Karen? Not even close.
“Karen. Just to be safe—coupling practice can still strain your body.”
“I know that. Don't worry.”
“Yeah?”
Since it mimicked coupling, mismatched wavelengths could definitely take a toll.
“...Here we go.”
With those words, Netoru felt mana flowing down from her through their connected hands. They said mana reflected a person's nature. Karen's felt crisp and refreshing, like a breeze over a lake surface. Mana this pure and refined... She really was one captivating girl. Netoru bumped up his evaluation of her another notch.
And yet, a deep regret lingered in one corner of his chest. A flawless white canvas like her, and he hadn't been the first to mark it. As a man, as a coupling partner—it stung.
Obviously, the first mark on Karen's canvas had been Natsuo. Three years as coupling partners? No question.
“...Netoru. What're you thinking about? No distractions—focus on me.”
“Ah, sorry. Got it.”
Was it that obvious? Or just women's intuition? Under her dissatisfied gaze, Netoru snapped to and apologized.
He gripped her hand harder. Something like an invisible, intangible line formed from their joined hands. The mana path linking their mana nerve systems.
Karen must've felt it too—she let out a tense breath and murmured softly.
“Start gentle at first. Got it?”
“Don't worry. I'll go easy to start.”
With her low coupling wavelength, she was fragile as glass in more ways than one. Had to handle her with care.
“More than that, Karen—relax your body. Tensing up like that just makes the mana path unstable.”
“...It's my first time with you, that's why. Anyway, don't worry and hurry up. I've done coupling practice plenty.”
“With who?”
“Who else? Natsuo.”
Yeah, Natsuo. He knew, but asked anyway.
Netoru channeled mana into her through the connected mana path, just like when controlling a Holy Knight.
“Ngh...!”
A low moan escaped her lips, as if they were coupled. Then she greedily sucked in his mana, blending it with hers, and began activating her internal mana nerve system. Proof came as a faint glow emanated from the tattoo marking her mana nerve system on her lower abdomen.
Artificial coupling achieved. Now all Netoru had to do was supply a steady, moderate flow of mana without overwhelming her.
...Let's take a peek.
But sitting there like a fuel tank getting drained sounded boring. Netoru focused his awareness on his mana flowing into her through the mana path.
He planned to examine the structure of the mana nerve system built inside her body. One big perk of coupling practice: getting a look at your partner's mana nerve system.
His mana followed the flow she guided, naturally streaming toward her lower abdomen. It didn't take long to reach its destination—her mana nerve system, centered precisely at her uterus.
...So this is Karen's mana nerve system.
In his mind, dozens, hundreds of lines curved and branched repeatedly, forming a beautiful pattern. The structure of Karen's mana nerve system.
A mana nerve system was totally different from the regular nerves humans used to sense external stimuli. It was just a tool—an artificial organ—for processing mana efficiently and effectively. Back in the era of swords and magic without Holy Knights, knights used it to unleash superhuman power. Now, it powered Holy Knights. That's why output and efficiency varied between female pilots.
Netoru examined Karen's mana nerve system closely. Not that it meant much. He made a habit of checking his coupling partners' systems whenever he got the chance. Studying the mana nerve structures inside women's bodies might prove useful someday.
“......?”
That's what he was doing—browsing her mana nerve system out of habit—when he felt an odd incongruity. He tried to brush it off at first, but probing someone's body with mana naturally revealed a lot about them. That's how he realized the truth, leaving him stunned.
...No way?
For some reason, there were no traces of a mana path ever forming in her lower body.
And what that meant was simple.
Karen was still a virgin.
Despite three years with a coupling partner.