Note: The only actual exposure to High School DxD I have received is through fan fictions. I am ashamed to say I have neither read nor watched the legendary ecchi series, and thus most the details will (probably) be incorrect.
The inspiration for the concept of Neutral Ground comes from the bar in the Dresden Files.
Still, hope you enjoy.
Ophis glared at the humongous dragon in front of her- it, really- daring it to make a move. It was not the first such altercation between the two beings, drastically different in appearance. On one side was a little girl with long black hair dressed in a matching gothic lolita outfit, while on the other was a dragon that could only be described as gigantic. It was a being that could have used skyscrapers as disposable toothpicks.
"... Leave."
The dragon sighed.
"How many times have you said that to me already? For that matter, how long has it been since you started pestering me for 'silence'?"
"... That's not relevant, Baka-Red."
The dragon threw up its hands (front-paws?) at the loli's response.
"Fuck it. You know what? I give up. You win. Take the Dimensional Gap. I'm leaving. I'm sick of your constant nagging and all the attempted murder and explosions."
Ophis blinked. This was not an outcome she had expected, not by a long shot. And she'd been getting ready to permanently drive him out by force, too- she even had her own little army.
"... Liar."
"No, no, I'm perfectly serious. See?"
The dragon forced open a dragon-sized tear in reality in front of him to make a point. Ophis's eyes narrowed. On one hand, she couldn't sense any deceit from him, but on the other, Great Red would never simply relinquish the Gap like this.
By the time she refocused on what was happening, Great Red had already put half of his body through the tear. The dragon stuck his head back out of the tear.
"I might step back in here every now and then, but the Gap's yours now. I'm not going to linger. So goodbye, sucker!"
And with that, he was gone. Ophis was not naive. Unadjusted, perhaps, but not naive. But she was also not one to look a gift dimension in the mouth, so she closed her eyes and enjoyed the sensation of nothingness.
"Hey, you hear about that bar that opened up recently?"
Issei Hyoudou's life had most definitely improved since he had been resurrected as a devil by his Buchou, Rias Gremory. Sure, the fact that he had to die beforehand sucked, but now he had a legitimate excuse to be close to Rias-senpai's magnificent op- Rias-senpai. Not to mention the fact that he also got to be close to Akeno Himejima, the second of the Three Great Ladies of Kuoh Academy.
His newfound status as a devil did not mean that he had to give up on his social life. Previously, he had been the third member of the Perverted Trio, a universally-disliked trio of boys whose chief activities consisted of peeping and discussing porn. Right now, he was sitting with the other two members- Matsuda, a boy with a shaved head, and Motohama, a glasses-wearing pervert who could tell the three sizes of a woman at a single glance.
"What bar?"
"Some guy opened a bar on the outskirts of Kuoh proper, and it's really popular, so I've heard."
Motohama was busy telling Matsuda all about the latest rumors and information that came through the halls of Kuoh Academy.
"Why are you even interested? You're both obviously minors. They're not going to serve you anything."
Issei interjected.
"That's the thing. They don't just serve alcohol there, they serve everything from coffee to smoothies, too!"
Matsuda had a dreamy look on his face.
"Imagine being served coffee by a beautiful waitress in a uniform that shows just the right amount of cleavage... And when she turns around to leave the short skirt reveals a nicely shaped ass!"
The other two drifted off into their respective imaginations, drooling over perverted fantasies involving cute waitresses.
Sona Sitri, also known as Shitori Souna, had a headache.
She'd marked a stray devil for death just a week ago, and now he had simply vanished. But that wasn't what concerned her- it was the way he had vanished. The trail ended at a newly-opened bar on the outskirts of Kuoh, and she was curious what kind of existence could simply make a stray devil disappear like that. She knew there weren't any devils lurking around in the area- not on the books, at least- but she had a hard time figuring out what else it could be. Perhaps one of Azazel's lackeys? Of course, it could be just a dispute between two stray devils that led to a fight only one of them walked out of, but the fact that the bar was still standing contradicted that.
She reached for her phone, and dialed a number she had dialed many times before.
"Rias? I need a favor from you. Could you check out a bar for me? Bring your peerage, just in case..."
A small chime placed over the door rang as it opened, admitting a group of teenagers into a dimly lit bar.
The establishment was not very big, and had only three tables with four seats each, with six more at the bar. The bartender was a large, tanned, gruff-looking man with closely cropped red hair and beard. When he looked at the newest arrivals, something flashed in his tired eyes, and he put down the glass he was polishing to clap his hands together.
"Everyone out! Now!"
The customers left one by one, grumbling. The bartender pointed at the teenagers.
"Except you. You lot, stay."
The six teens- four girls, two boys- took their seats at the tables. The bartender crossed his thick arms, with a dusting of red stubble, and frowned.
"What are six devils doing in my bar?"
"We're here to investigate. A stray devil went missing around here, and we thought you might know something about it."
Said the blond-haired boy- Kiba Yuuto.
"Oh? And if I do know something?"
The bartender smirked slightly.
"Then you'll tell us, or we'll-"
A brown-haired boy- Issei- began, before a red-haired girl- Rias Gremory- put her hand over his mouth.
"Don't antagonize him, Issei. If he considered us our enemies, we'd all be dead."
"Looks like you've seen through my disguise, missy. What gave it away?"
"The oppressive feeling of power throughout the entire bar is faint, but noticeable. I've felt many different suppressed auras before, but yours is in a completely different league. Secondly, your hair color. There just aren't any other tanned, red-haired individuals like yourself in Kuoh. Lastly, the name of the bar. 'Crimson'? Really?"
"I was never one for originality."
Issei looked from the bartender to Rias, confusion written on his face.
"Buchou? What's going on? Who is he?"
The redhead's mouth was set in a grim line.
"He is Great Red, Dragon God of Apocalypse and the current strongest being in existence."
The reveal sparked mixed reactions from the devils.
Issei paled, and shrunk back into his chair, gulping. Kiba materialized a sword and stood up, getting into a combat stance. Akeno stiffened and began focusing, sending a faint scent of ozone through the air. Koneko got up on her chair and mirrored Kiba, fists held at the ready. Even Asia, the newest devil inducted into Rias's peerage, had a scared expression on her face, although her lack of combat capabilities made it difficult for her to do anything else.
Seeing their reactions, Great Red sighed and brought his palm to his face in a gesture of resignation.
"Look. I'm not here to cause havoc or anything like that. You all know that if I wanted to do that, the entirety of Kuoh would be lying in ruin right now. So calm the fuck down, won't you?"
"That still doesn't explain why you're here. Weren't you fighting an eternal war against Ophis, the Dragon God of Infinity?"
"I got tired of putting up with her shit and decided to leave. What, got a problem?"
This time it was Rias's turn to execute a perfectly timed facepalm.
"Yes, I do have a problem. The strongest being in existence just casually strolls into Kuoh and starts up a bar, without notifying any of the residents? Can you even imagine the paperwork that would need to be filed for this? Ugh, Sona's not going to be happy. Not at all. At least we know what happened to that stray devil- you took care of him, didn't you?"
"He tried to trash my bar. I just made him pay for it. With his life."
"What's with this place, anyway? Why a bar?"
Said Akeno, frowning.
"I wanted to make a place where any of the different races could meet without going at each others' throats under the eyes of a watchful supervisor- namely, me. I like explosions and death, but only when I'm the one doing it. Plus, it's always fun to watch their reactions when they realize who I am."
"So... A neutral ground of sorts? You do realize that all the factions will try their damnedest to sway you to their side?"
The bartender shrugged.
"What do they have that I don't? Unless they can promise me, say, another Dimensional Gap, I don't think they'll really have any weight to throw around in negotiations."
"Well... Good point."
"Now, are you going to order or not? If you're not, then stop loitering and leave."
As the group hesitantly made their orders, Rias had one more question for Great Red.
"Are you actually male, or are you just in this form for convenience?"
"Oh, you mean am I capable of blurring the line like that tranny Infinite dragon? Yes I am. Why, would you be more comfortable if I was a woman?"
And with that Great Red turned into an absolutely stunning woman with long, flowing locks of red hair, and a surprising resemblance to Rias. But what captivated Issei's attention wasn't that- it was the boobs. Large, barely restrained by the collared shirt she was wearing, and most definitely an E-cup at the very least. Blood began trickling from his nose, all of his previous apprehension forgotten.
Rias looked at her Pawn, and sighed.
"Please stop teasing him- just take whichever form is most natural to you. Please?"
The other redhead pouted.
"I don't think you're in any position to make demands, young Gremory, but I'll do it only because he looks like he's going to die of blood loss pretty soon."
The beautiful woman was gone, replaced by a childlike girl in a red-and-white gothic lolita outfit, this time bearing a striking resemblance to Ophis, her hated enemy. In fact, she looked just like Ophis, but with red hair, tanned skin and red clothes.
"This... Is your natural form?"
"Not really. That damned loli-hag Ophis and I are linked in a sense- we were created together, after all- so her form kind of leaked over. As much as I dislike admitting it, this form has its uses. For one, it takes a lot less energy to make than an adult form. And it has the added benefit of making some opponents I face lower their guard, although if they already know who I am then that's kind of useless."
Said the red-haired loli, plucking at her dress.
"Buchou. What do we report?"
Koneko said.
"I... Honestly don't know, Koneko. Whatever we report, it'll doubtless draw the attention of every faction around, since rumor's going to spread that Great Red's set up shop in Kuoh. I have the feeling our lives are going to be a lot more hectic from now on..."