Hibiki opened the door to the factory and looked around at the various doors lining the hall. She scanned each one as she walked down the hall, checking the label for each door as she looked for the specified room. Seventh from the entrance, near the end of the hall, was the door in question, labelled R&D. She turned the handle, pushed it open, and stepped inside.

As expected, Yuubari was there, wearing her yellow jumpsuit. She had asked Hibiki to come see her, stating that she had something she wanted to test out. Of course, knowing Yuubari it could be anything.

"Ah, Hibiki-chan, you're here! Excellent. Now, we just need to wait for the other to show up. Shall we get started, though? Both to warm you up and to kill some time?" Yuubari said as soon as Hibiki walked in.

"What do you mean?"

"You horny? I sure hope so, or I'll have to find someone else to test this on."

Hibiki shrugged. "I'll help you. Do you want me to undress?" she asked, and Yuubari nodded. Hibiki unzipped her skirt and removed it along with her panties, and neatly folded both and set them aside. She was soft, her small penis and balls tightly clutched together under a small patch of fuzzy hair. She held her hands behind her back and looked to the side, a little self-conscious.

"I'm gonna use my hands to get you all warmed up, alright?" Yuubari said, and Hibiki nodded. Yuubari got straight to work and started stroking and caressing Hibiki, making her cock slowly harden. After a minute or so she had grown to her full four inches, the rod softly pulsing.

"All ready?"

Hibiki nodded.

"Great. Okaay, I'm just gonna keep you up, but you can't cum, alright? You gotta tell me if you're about to pop, got it?"

"Khorosho."

Yuubari smiled and started stroking Hibiki with just a finger, enough to maintain Hibiki's erection. Some precum began to build up and Yuubari licked her lips. "You and the other girl are gonna enjoy this so much, as long as it works the way it should."

"Who else is coming?"

The door opened just as Yuubari was about to answer and in stepped Inazuma, who froze and blushed when she saw what was going on. "Hawawawa! I'm so sorry! I didn't mean to barge in!"

"Inazuma-chan, hold it! You're just in time, Hibiki's already worked up. Come on, I invited both of you here to test out something I've been working on. Close the door" Yuubari said, and Inazuma reluctantly shut the door. She walked over to stand next to Hibiki, though she tried not to stare so much.

"Before we begin, I want you both to know we can stop any time you want. Got it? Both of you, if it doesn't feel good, or you just don't want to continue, just say the word. Even now, if you want to leave, I won't stop you" Yuubari said, and Hibiki and Inazuma shared a look.

"I'm already turned on. You're mean if you'd work me up like that and then stop."

"Hawawhat? We're both gonna..." Inazuma said, unable to finish the sentence.

Yuubari grinned and lifted something off her work table. "Check out this!" she said. It was rubber and clear, about six inches in length, and cylindrical. "It's an artificial vagina, similar to the onaholes you two have seen around base. Only this one is double ended, so two girls can be in it at the same time!"

The two futas took a few moments to look the sex toy over, noting it was around six inches in length and appeared to be ribbed on the inside. "Please hurry" Hibiki said as she rubbed a thumb on the tip of her penis.

"OK you two, face each other" Yuubari said, and the two girls did as told. Yuubari approached, applied a generous amount of lube to both ends of the toy, and pushed it onto Hibiki's cock. Hibiki let a sharp breath as the pleasure shot through her, and Yuubari turned to Inazuma. "Your turn."

Inazuma nodded and lifted the front of her skirt. She pulled down just the front of her panties and her stiff cock sprung free. She let the hem of her skirt rest on top of her penis, preserving as much of her modesty as possible. She pushed her hips forward and her cock entered the other end of the toy. "OK, you're both around four inches, right?"

"Khorosho."

"Um, I think Hibiki-chan's a little thicker-nanodesu."

"That's OK, the toy should still work. Ready? Alright, here we go" Yuubari said, and she began to run the toy back and forth. Hibiki and Inazuma had the tips of their penises pressed together, with the toy holding both in place.

"HAWAWAAHH!" Inazuma yelled, and covered her mouth. Hibiki let her head roll back a bit and she grabbed the hem of her skirt with her hands. Their combined length was roughly eight inches, so the toy had plenty of space to slide back and forth over the two of them.

"So far so good! Girls, everything alright?"

"Khorosho."

"This is r-really lewd...nanodesu..." Inazuma said through her hand. She was watching the toy as Yuubari stroked it over the two cocks, her body shaking. Hibiki, for her part, was quietly enjoying the experience.

"I probably should've put condoms on both of you, this is gonna be super messy when it's all done. What do you two think?" Yuubari asked, and Hibiki opened her eyes.

"Hawa... OK..."

"Alright girls, go ahead and pull out so I can get the condoms on" Yuubari said. The two of them held in place for a few seconds before they reluctantly pulled out of the toy and Yuubari set it aside. She watched the two of them stand there with their twitching cocks, glistening in the light, begging for attention. Yuubari fished a few condoms out of her jumpsuit pockets and wasted no time applying them to her futa test subjects.

"Okaay! Here we go again" Yuubari said, and slid the toy back onto Hibiki's cock. Inazuma put hers back in and Yuubari resumed the stroking, little sound in the room beyond the labored breathing of the futas and the soft shlicking of the toy.

"Hey, here's an idea. How about I hold the toy in place and you two thrust in and out of it?" Yuubari asked, and the futas looked up at her.

"I don't think the toy is long enough for that. When one of us is all the way in, the other only has her tip inside. It'd be kinda frustrating" Hibiki said.

"Hmm, you think so? OK, I'll make another one later and make it longer. Would you two like to come back in a few days and try that one out?" Yuubari asked. Hibiki nodded, and Yuubari turned to look at Inazuma.

"Y-yes, YES! Haahwawhaah!" Inazuma yelled. She covered her mouth again and screamed as she started cumming, filling the condom within seconds. Yuubari licked her lips and kept pumping, hoping that Hibiki would finish soon too.

"Hah... Ahh! AAHH! Oh gosh, Yuubari-san, s-stop!" Inazuma said, and Yuubari stopped. Inazuma pulled out of the toy with a yelp, her stiff cock bobbing. "Wuh... Way too intense-nanodesu..."

"I'm sorry, Inazuma-chan. If you want you can sit down and take a break, OK? Hibiki-chan isn't done yet" Yuubari said, and Inazuma found her way to one of the chairs in the room. Yuubari felt Hibiki buck her hips and she turned her attention back to the other girl.

"Keep going please."

"Heh, I love when they get needy."

Yuubari stood next to Hibiki and started pumping again, and Hibiki pushed her hips forward, trying to get more of herself into the toy. She was breathing hard through her nose, her hands tightening around the hem of her skirt. "Khorosho... Khorosho..."

"Gettin' close? You don't have to hold back. Inazuma certainly didn't" Yuubari said. "Come on, quick. Cum cum cum cum."

"Khorosho... Gonna... S- Stop. Stop!" Hibiki said, and Yuubari pulled the toy all the way down as hard as she could, as much of Hibiki's cock buried deep inside as both of them could get it, and Hibiki came. Silently she fidgeted and squirmed through her orgasm, her cock flexing hard against the silicone. Her orgasm quickly ended and Yuubari kept the toy in place, knowing that Hibiki would want to eke out every last bit of pleasure she could.

"...I like your toy" Hibiki eventually said, and Yuubari grinned.

"Heh, glad to hear it! Now, why don't you go join your friend? I'll get you two cleaned up in a sec" Yuubari said, and Hibiki nodded. She watched her walk over to the bench Inazuma was resting on, their wrapped cocks still pretty hard. Yuubari wondered if they wanted to go again but decided they'd really benefit from a break. She got the condoms pulled and the girls wiped off and she put the toy in the sink.

It was fair to say the first model was a resounding success, and Yuubari knew exactly how best to implement this new design. She'd enlarge and lengthen the design and adapt it into a double-ended onahole, that way the one onahole could be installed in the bathroom walls and two girls could use it at the same time, one in each bathroom. A few modifications to make it compatible with the base's onahole self-cleaning system and Yuubari would be the most popular non-volunteer on the base.

Better get started. This is gonna be so awesome, I can't wait to see how popular the final design is. Onaholes will never be as popular as volunteers but that's OK, these will still be awesome.

"Yuubari-san."

Yuubari looked over her shoulder and saw Hibiki and Inazuma standing next to each other, with Inazuma's hands behind her back and Hibiki's hands holding up the front of her skirt. She looked down and saw that both girls were still stiff and twitching, some precum already building up again. "Um, could you please... Nanodesu..."

Yuubari licked her lip and picked up the prototype double ended onahole. "Just let me get this cleaned out girls and I'll be right with you both."

"Khorosho."

"Nanodesu."

A couple more rounds won't hurt Yuubari thought. After all, an experiment is most successful when it's run multiple times. You get the best results that way~