Hyperdimension Neptunia is owned by Compile Heart, Idea Factory, Sega and whomever else worked on it.

Random idea is cleared for launch!

Nepgear tilted her head in confusion. "Um, IF, have you noticed anything different about big sis lately?"

"You mean how she caught up on the large backlog of paperwork, did more than a hundred quests and isn't cracking jokes every five seconds?" IF asked as she cracked open a can of a fizzy drink as Nepgear nodded. "Yeah, she got kidnapped by an aliens and was replaced by this."

"WHAT?!" Nepgear gasped in surprise. "We need to save her! And how did you know?!"

"I saw her get kidnapped." IF told her. "And the aliens haven't gone anywhere." She pulled out a phone and pushed a button, showing a satellite feed. "We're just trying to figure out how to get into space. Your SpaceGearDam is still broken."

"But..." Nepgear teared up. "I miss the cute and funny big sis. I don't know what to do if she gets all serious."

"Well, she hasn't tried to feel up my chest since we brought her back." IF commented. "Look, if you want to get Nep back faster, you should fix your SpaceGearDam."

Nepgear nodded and turned to rush to her lab when Neptune, the alien one, appeared in front of her.

Really, when Nepgear looked closer, she could tell this one wasn't her big sister.

After all, the eyes were green, her hair clip was off-center and most damning of all?

She had a plate of steaming eggplant slices in her hands!

"Do you want some eggplants, Nepgear?" The fake Neptune asked with a smile.

"Uh..." Nepgear smiled nervously as she took one. "Sure..?"

The fake smiled and put the plate down on the table before taking a slice and munching on it while walking away. "Eggplants are healthy and good for you."

"...Okay, that was beyond freaky." IF said as she nodded. "Don't worry, Gear, I'll keep an eye on the alien craft and the fake while you get the robot fixed up."

Nepgear nodded and rushed to her lab. "I hope big sis is okay."

(-)

Some time later in Nepgear's underground lab...

"Alright! It's taken me three months, three weeks and three days..." Nepgear groaned and hung her head. "I've been influenced by Histy too much," she shook her head. "But no matter! The SpaceGearDam MK II is ready!"

Compa's eyes sparkled as she looked at it. "Ooooh! It looks like Nep Nep's HDD jet form!"

"...That's because it is." Nepgear sweat-dropped. "I kept running into issues of my Nepgeardam not being aerodynamic enough to obtain escape velocity, so I threw the whole thing out and just built a large fighter jet."

"...How long did that take, Gear?" IF asked and Nepgear laughed nervously. "Gear?"

"Two days."

IF groaned and slapped her face. "You mean you could have had this done in two days?!"

"Well... No." Nepgear smiled nervously. "The plot wouldn't have allowed it." IF and Compa both face-faulted at the casual breaking of the fourth wall.

Histoire, who was in the room, merely sighed. "Can we keep the pod person?" Nepgear gave her a hurt look and Histoire's face flushed as she shook her head and waved her arms. "I don't mean that we shouldn't save Neptune, but the pod person has been so efficient at everything that our Shares are at an all time high," so much so that Noire and Blanc were accusing them of having some sort of share-stealing machine, "I estimate that even if Neptune was as lazy as she normally is that our shares will be fine for three years."

"See?" Nepgear smiled as she got into the fighter jet. "I'm going to go save big sis now!"

The ceiling opened up and the floor flipped the jet up to point straight up while IF, Compa and Histoire all ran away from the jet as it powered up and launched itself into the sky.

"Well, that's that..." IF said as she turned to see the fake Neptune standing there. "Uh..."

What was shocking was that she looked sad.

"Do I need to go now?"

Compa tapped her chin. "Hmmm... Oooh! Histy! We now have another Nep Nep! She's not bad, is she?"

"Hmm..." Histoire thought about it... For three seconds. "We'll figure out what to do when Nepgear gets back."

(-)

Nepgear flew straight up and eventually burst through the atmosphere. "Wow, space is so..." She shook her head and gasped as she saw a flying sphere between Gamindustri and the moon. "Hang on, sis! I'm coming!" She hit the thrusters and launched herself into the sphere before firing on it to punch a hole in it and she flew straight into it.

After landing the jet, Nepgear jumped out and started rushing through the sphere ship until she came across a room. "Neptune!" She gasped as she saw her sister...

...Who was sitting on a couch, surrounded by green, humanoid aliens, while playing Lowee's mascot fighting game.

"Oh! Hey, Nep Jr.!" Neptune's eyes lit up as she put down the controller and flipped over the couch. "See? I told you that my kid sis would come for me." The aliens nodded as Nepgear rushed over and hugged her tightly. "Woah! Did you miss me?"

"Are you okay?" Nepgear asked as she let go and the two walked out of the room.

"Oh yeah." Neptune smiled as they made their way to the jet. "They were really nice. Other than their examination." She pouted and rubbed her butt. "I told them that they didn't need to poke my butt so much to get readings."

"Uh..." Nepgear sweat-dropped. "They didn't... Shove anything in there, did they?"

"A thermometer." Neptune told her and Nepgear's sweat-drop increased in size. "Anyway, Nep woah! That jet looks cool! Can I fly it?"

"Sure." Nepgear nodded as they got inside, turned around and flew back to Gamindustri.

The aliens looked at each other and shivered before pushing a button on the console.

'Trying to take over this planet would be impossible, the people are crazy.' one of them said to the other one.

'Should we just destroy the planet?'

'You saw what happened when we tried to probe her, our machines broke. What if they can breathe in space?'

'Good point, let's leave this planet.'

'What about pod 87423?'

'Leave it. Maybe it will be fortunate enough to survive.'

The aliens flew off and Gamindustri had no idea how Neptune had saved them all from conquest or death.

The fake Neptune somehow ended up living in Leanbox with Vert, both of whom enjoyed a pleasant life with each other that involved video games and lewd cuddles.

But that's a story for another time.

How did I not do this plot before?

And yes, Nep got probed in the stereotypical way, but thought it was a thermometer.