"Wait... what on earth are these!?"
After Juju agreed to temporarily hand over the ownership of her rear to Rin Ito, he pulled out a row of rods of varying sizes from a bag and lined them up from smallest to largest.
"Ahem..." Rin cleared his throat with a look of mock seriousness. "Juju, you need to understand that developing the body isn't a joke. If done wrong, you could get hurt... You wouldn't want to be lying in a hospital bed, and when someone asks why you're there, have to say you were hospitalized because your ass tore during development, would you?"
Rin wasn't just talking nonsense. Without the system's reinforcement, given Juju's petite frame, even "normal" activities could cause injury, let alone this.
However... Rin's smirk widened as he shifted the topic.
"But then again, if it really did tear, that would count as losing face in front of Shinju... Plan success?"
"I don't want that kind of embarrassment!"
Juju, like Shinju before her, became a "crotch-staring cat" for a split second. She had originally expected Rin to "develop" her using his actual body like in a doujin, but now she was genuinely afraid of splitting open.
"First, let me observe the specific situation properly... Take off your skirt and lie on the sofa with your butt up."
"Uuu..." A short whimper escaped Juju's throat. Though she was expectant deep down, the shame was just as real.
Biting her lip, the blushing Juju unfastened the hidden clip at her waist and slid off her red pleated school skirt, revealing her pure white cotton panties. Once those were removed, the girl's most guarded secrets were fully exposed to Rin.
But... it wasn't enough.
Juju climbed onto the sofa, grabbed a throw pillow, and buried her face into it, assuming the humiliating "OR2" (all-fours) position.
Rin gripped both of her slender butt cheeks and pulled them apart firmly. Now, every hidden inch of the girl was laid bare before his eyes.
Rin patted her thin cheeks. "Don't let your hands stay idle. Hold them open like this."
"Pervert..."
After a muttered curse, Juju let go of the pillow and used her own hands to pull her cheeks apart. Rin leaned down slightly.
There was no unpleasant odor on her; instead, a faint, clean fragrance wafted up—the scent of body wash.
She must have showered back at the studio before coming... No, it wasn't just a shower. She had definitely given her interior a thorough cleaning as well.
"Mmm... it's a healthy pink. And it's twitching... Are you that excited, Juju? Puff~"
"EEEYAAAHH!!! Wh-why are you blowing air on me!"
Juju's voice trembled. That sudden shiver of electric sensation made her entire body tense up, and she felt something being squeezed out from her depths.
"Just testing your sensitivity." Rin reached out and lightly smeared the moisture on her tender flesh. "Definitely a zako."
"I..." Juju wanted to argue, but she was powerless. She could only bury her face deeper into the pillow.
Between her previous performance and this one, "zako" was the only appropriate word... Reaching a climax and passing out just from watching Marin lick his fingers made her more of a pathetic weakling than the average girl.
And now... just a puff of air on her rear made her start leaking.
"Great sensitivity. Next is the digital exam. It looks cute and pink on the surface, but there might be internal issues."
"!!!!" Juju bit her lip hard. She had never experienced this, but she had seen similar things while scrolling through videos.
A digital exam was a standard medical procedure, but she knew he wasn't planning anything "regular."
But... it was for her sister! She had to endure!
Yes, for Shinju!
Having convinced herself, Juju tilted her petite butt even higher.
Rin, guessing she had already cleaned herself, still tore open a condom and used it as a finger cot over his index finger. And then...
Thrust!
"UUU-EEEEYAHHHH!!!!"
The strength of her rear was no match for a finger. With the lubrication from the latex, Rin's finger slid inside with ease. For the first time, her "exit" had become an "entrance."
"Mmh... no strange bumps. Feels very healthy. A good chance to let you get used to the feeling."
While toying with Juju, Rin noticed the tips of her fingers—which were still holding her cheeks open—were turning white from the force of her grip. Powerless to resist, she could only bite the pillow to keep her shameful noises from escaping.
However... how could Rin let her off that easily?
A digital exam only required one hand. Rin still had another one free.
With one hand checking the back, the other hand was obviously going to play with the front!
"!!!!!"
Under normal circumstances, not many people derive pleasure from the rear, but Rin was performing a "double-stimulation" training. Even though Juju was a virgin, her most sensitive spot was completely exposed to Rin's hand.
Humans are animals, after all. Through this method, Rin could form a Pavlovian response in Juju, ensuring that pleasure was associated with both sides.
"GUH!!!!"
Her sensitive body was being toyed with against her will, making her instinctively try to pull away. But Rin's hooked index finger kept her pinned. She could only grip the sofa cushions with both hands, enduring the mounting waves of pleasure.
Her legs could no longer support her. Her small rear shook uncontrollably, and her slender feet—still clad in black thigh-highs—thrashed around helplessly as her ten toes curled tight.
Her petite frame spasmed. The noises coming from her throat weren't tsundere insults anymore, but pure, wanton moans. While she barely managed to stay conscious—unlike that day in the parking lot where her eyes rolled back—her body was vibrating with tremors.
As his palm grew hot and wet, Juju's body gave one final, violent jerk before going limp. Saliva soaked the pillow she was hugging and dripped onto the sofa by her legs.
Rin withdrew his finger. The latex "cot" remained clamped tightly within her.
He gave her butt a playful little slap before heading to the bathroom to wash his hands. It took quite some time for Juju to regain her senses.
"Hmph... pervert! Satisfied now?"
"Tch, tch... why call me a pervert? You were the one who begged me to train you. I was doing you a favor by checking your health. I've checked with my finger—you're perfectly healthy."
Rin had been checking more than her health; he was looking for her internal sensitive spots. He discovered that even through a layer of flesh, the closer he got to her "baby room" (womb), the more sensitive Juju became.
It seemed Kaede's previous "training" had been very effective.
Faced with Rin's teasing gaze, the beet-red Juju had no rebuttal. She puffed out her cheeks and looked away.
"I... hmph. If the check-up is over... can we actually start!?"
"Of course..." Rin walked back into the room with some cleaning tools. "First, the thing you need to learn isn't expansion, but cleaning. I can help you here, but development takes time. Once you go home, you need to know how to do this yourself."
"It's simple. First, squeeze the air out of the tube..." Juju was smart; she understood the mechanics after one explanation. "Want me to help you with the first time?"
"NO! I'll do it myself!!!!!" Juju's neck turned red as she snatched the enema gear from Rin's hand.
Back at the studio, Marin had helped her a few times. Juju's role then was simply to tell Marin when she couldn't hold it anymore, have Marin leave, empty herself, and then let Marin back in.
Though she had never done the actual "insertion" part alone, she definitely didn't want Rin's help. If he helped, he'd surely stay and watch her until she couldn't hold it anymore!
Emptying herself right in front of him would be a thousand times more humiliating than being fucked by him!!!
"Fine then... I'm going home to grab a few things. You get started on the cleaning."
Rin didn't push. Given Juju's tsundere pride, he had to give her some modicum of dignity during the training. Besides, he really did have items to fetch.
Kaede had previously redeemed quite a few toys and left them at home. Those system-made toys were like the "tokens of love" he gave the Nakano sisters—they could monitor detailed physiological data and had more "functions" than standard toys.
To truly train her, he needed the system-grade gear.