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English
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Published:
2025-08-31
Updated:
2026-02-09
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123,798
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24/?
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Humans and Demons

Summary:

In 1917, Jonathan Joestar arrives to Japan, searching for a lost friend who was researching things men were not meant to know. By happenstance, later in 1917, one Kamado Tanjiro loses everything but his sister and sets out to turn her back to normal. Even if two don't cross each other's path immediately, they're destined to meet.

At the same time, in 1917, one Dio Brando also comes to Japan and after checking the surroundings, decides to pick a fight with the so-called Demon King.

Notes:

Chapter 1: Two Foreigners

Notes:

(See the end of the chapter for notes.)

Chapter Text

It is well-known that the Empire of Japan and the United States of America had good relations at the turn of the 20th century. Commerce has been thriving for years, to the point that in 1908, a group of distinguished Japanese business leaders, such as Shibusawa Eiichi, 1st Viscount Shibusawa and the founder of the First National Bank of Japan, met the first official U.S. business delegation.

As it happens, 1908 is the year when an enterprise under the title of Speedwagon Oil Company has been founded in the U.S.

 The lucky oil tycoon behind it, a British man named Robert E.O. Speedwagon made waves with his wit, charm and business savvy which quickly became legendary in certain circles. His rapidly expanding business branched out, in both its functions and its locales.

Speedwagon Foundation, established in 1910 in the name of medical research and environmental conservation, set one of its first offices abroad in Tokyo City in 1914. Mr. Speedwagon himself attended its grand opening, shaking hands with people like Dr. Wada Keijuuro, a researcher who aimed to review ancient medicinal practices of the country with modern methods and bring something brand-new and enlightening to the world.

If one was to study the pictures regarding that event from newspapers of the time, they would likely note a very remarkable man standing right next to the charitable scarred oil tycoon. A tall man with a very broad build, who, nonetheless, was dressed in the finest cloth and carried himself gracefully despite the bulk.

This man sets his foot on Japanese soil once more today, on March 16th, 1917. His name is Jonathan Joestar.

“Quite honestly, I’m surprised how well you speak the language, Joestar-hakase,” a youthful driver, Hiroaki, chats with the man as he carts him and his wife around Tokyo. The driver then winces and bashfully apologizes, glancing for a moment at the couple behind him into the front-view mirror. “Sorry, I mean, I heard Westerners find it very difficult to learn.”

The man with dark hair that almost seems to gleam with indigo color under certain angles chuckles and fixes the lapels of his formal brown jacket.

Streetlights of Tokyo illuminate his face as the car drives through the night city. A trip from the port in the Fukagawa district where the Joestars arrived would have normally taken a good part of the day, or, rather, night, by foot, but that’s the thing about the Speedwagon Foundation. It’s outrageously wealthy and spares no expenses on comforts of its employees and associates.

Hiroaki himself has a custom, form-fitting and very comfortable uniform with the Foundation’s logo on the cap, the logo even adapted into Japanese, and the Joestars, esteemed researchers, have a car drive them right to the Foundation office in the Nihonbashi business district, even in the middle of the night.

“It would be very presumptuous and rude of me to arrive into a country with an intent to stay without knowing at least the basics of the local language,” Jonathan hums. His accent is noticeable, but his grammar is impeccable. “And Japanese is very difficult, Hiroaki-kun, that much is true. However, learning it has been a worthwhile endeavor.” 

The man then feels the nimble fingers of his dear wife, Erina, playing with his messy ponytail.

“We would have been here much, ah… sooner, but I didn’t pick it up nearly as quickly as JoJo,” Erina adds, stumbling in her wording and with an accent much thicker than Jonathan’s own, yet her message is very clear.

For a moment a thought crosses Hiroaki’s mind about the age difference of the couple. Jonathan doesn’t seem that much older than himself, late 20s, maybe early 30s, and Erina, while graceful and beautiful with barely a wrinkle on her pale face, doesn’t hide a streak of gray beginning in her hair. The couple is well-dressed and carry themselves gracefully, like aristocrats, not that the driver has seen many of those, and he thinks about uneven marriages of the wealthy people.

Then Hiroaki shakes himself, it’s an unbecoming thought.

“So you’re here for research, Joestar-hakase?” the chatty driver asks, tilting his head while still keeping eyes on the road. It’s not like there are many cars to worry about, for there are few dedicated car roads around, but pedestrians and public tram transports. In fact, he has to stop the car as a tram passes right in the intersection they drive through. “I don’t know what you’re going to unearth here. You’re an archaeologist, aren’t you? I don’t think we have, like, di-no-saurs to dig up here.”

The way the exotic foreign word is pronounced by the young man in English makes the researcher chuckle again and Jonathan can’t help but to rectify the inaccuracy.

“It’s not that straightforward, Hiroaki-kun,” he begins and Erina shakes her head fondly, muttering in English.

There he goes…

The tram passes and Hiroaki pushes the gas pedal.

“Archaeology relies on cross-disciplinary research,” Jonathan explains. “Especially when the question is the analysis of excavated findings, which is exactly why I’m here. How do you explain a vase found next to a skeleton? Was it a personal belonging or a part of a ritual? One needs context, derived from culture. Like, say, local folk tales and legends. Though it’s an oversimplification, naturally.”

“Folk tales…” Hiroaki himself chuckles and grins. “You’ll find plenty of folk tales here, Joestar-hakase. Yokai, man-eating oni, we have a variety you Westerners likely don’t.”

The driver misses the sharp and aware glance the couple exchanges behind him.

“Man-eating oni, you say?” Erina asks curiously.

“Yeah, people in the country are really superstitious about stuff like that,” the young man continues casually. “Pretty much all the do’s and don'ts of behaving at night come from that. Keep to the light, carry a wisteria charm, that sort of thing. Dark ages, you would say.”

“Well, it will be interesting to learn where those legends take their roots from,” Jonathan hums, putting his large hand atop Erina’s as the woman grasps his knee, the only sign of her tension.

The rest of the way follows the same trend of Hiroaki dropping random trivia about Japanese culture without realizing it while asking questions about his passengers’ work.

By the time they arrive at the building boasting the large version of the logo on the driver’s cap, he’s surprised to learn both spouses are here for work. While only Jonathan boasts a recognized diploma, Erina is recognized by the Foundation itself as an experienced medical expert, having worked as a nurse in a variety of countries, from India, to her homeland, Britain, and other European countries, to the United States and Canada.

Erina is here to study the Japanese medical achievements and methods, while Jonathan, as they loop back to more than once, is here to study the cultural background to understand the Foundation’s latest archeological excavation findings.

“Best of luck in your endeavors, Joestar-hakase!” Hiroaki waves as the couple leaves for the office. It’s a tall dark building with the logo of the Foundation hanging about the grand front door. Quite a few windows sport lights, just like many other offices and businesses around, as despite the late hours, people are still working there, in one of the bustling districts of the grand capital city. Jonathan waves back at the driver with a soft smile before turning to discuss something with his wife as they go. The man opens the door for her and subsequently scares an office worker going home who hasn’t been expecting to see a giant of a man on his way out.

As he checks the notebook in the inner pocket of his jacket, Hiroaki knows his work isn’t done yet. His shift has another assignment before he can retire for the next two days. There’s another person, a Foundation science associate he has to accompany. Though he looks left and right into the car windows, he can’t seem to find the man fitting the description.

“Who that… Western gentleman might have been?”

Hiroaki almost drops his notebook in shock and quickly puts it back, taking a look in the front-view mirror to see the back seat. He never noticed the man arriving and quietly sitting himself down. It’s like he appeared from thin air.

His passenger wears an extravagant suit, with lapels of his black tuxedo embroidered with golden patterns. The shadow from his white fedora with a dark red ribbon that almost seems black covers the man’s face but doesn’t hide the brilliant red eyes that almost gleam right into Hiroaki’s soul even through the mirror.

“That… that was Joestar-hakase, the British archeology expert, sir,” Hiroaki answers, stumbling a bit. The other seems to notice his unease, giving him a smile and a soft smile. He raises his head and suddenly, the fedora no longer covers his face in shadows.

“Oh, have I startled you? My apologies, Hiroaki-kun. I’ve been told I have a quiet step,” the man says, leaning on the back of his seat in a relaxed posture. “My wife, mostly. Always startle her when she cooks.”

“Happens to the best of us, I guess, Minaguchi-san,” the driver chuckles, feeling a bit lighter and pushing the gas pedal to drive the associate researcher home. It’s far from the first time he’s been driving the man or his family around, yet somehow, he still takes him by surprise.

Hiroaki’s passenger gives a glance to the Foundation building before it disappears behind them, narrowing his eyes and murmuring to himself, so low the driver has no chance of hearing it.

“Joestar, then…”


According to the latest archaeological research, Chiba Prefecture, located south-southeast of Tokyo, has been settled since prehistoric times. Recently, this region has been militarized due to a war with one of the continental powers, in order to protect the capital of the Empire of Japan.

That said, this region sees some traffic of foreign tourists. Mostly for the views. If one is bored of the cultural landmarks of Tokyo or other cities inclined towards tourism, a stroll through the forests of Chiba is always a choice. The locals, however, will warn you of monsters lurking in the dark, the belief more wide-spread as one reaches the edges of modern civilization.

A Western man with jagged blond hair, sharp eyes of burning orange and three dots on his left ear, sporting a dark cape with feathers on shoulders, waves off concern an older couple shows him, instead inquiring curiously about where people go missing most often in the area.

“Are you… perhaps, a demon slayer?” the wrinkled woman asks hopefully, looking at the man so tall and strong it’s almost unnatural. “These forests out there are cursed with a demon, of that we’re sure.”

“Oh, I’m not a slayer, milady,” the man says with a chuckle, pressing a hand to his chest. “Though I am familiar with them. Perhaps, some of them will cross my path again. I thank you for your assistance.”

“And we thank you for hearing out our plight, young man,” the woman’s husband replies. “Please be safe in your travels.”

The mysterious man leaves the small village in the vicinity of Nikko.

He’s no demon slayer, but he’s more than aware that some monsters hiding in the dark are more real than others. He, of all people, knows the matter most intimately.

After all, Dio Brando is one of these monsters.

It’s been thirty years since he abandoned his humanity and became a vampire, an immortal creature hungry for people’s blood and living in the dark. Here, in the land of Japan, he’d be called a man-eating oni, a demon, but Dio finds the comparison unflattering and degrading to his refined being.

Fallen leaves rustle under his feet as he ventures deeper into the forest. The area is quiet, unnaturally so, with no wild animals emanating a single squeak because they know there’s a grander predator at large.

While initially intrigued by the rumors of beings even distantly rivaling himself, Dio quickly grew disappointed upon arriving to the Empire of Japan and witnessing those creatures first-hand. Most of them feral, possessing one-track minds and little thought beyond securing their next feast. Their cruelty is primitive and their powers are useless compared to himself, wasted on simple weak-minded fools.

Gorging on flesh, in Dio’s opinion, is also unbecoming, when he himself only needs human blood and, as such, can be much more efficient in infiltrating society and using humans in more ways than just a food source. Something those demon brutes don’t have the mental capacity to think of. 

The only thing of note about them are the Blood Demon Arts some of those creatures develop upon consuming enough human flesh. Party tricks, in the eyes of Dio who, after initial surprise, learned to pin these demons down to walls and trees, leaving them to burn in the sun for daring to challenge him.

Just as pathetic as the youthful demon slayers who dared raise their blades against him and pay with their lives in seconds.

As he reaches Mount Nokogiri proper, a low mountain in proximity to the Tokyo Bay, Dio finds something different.

It’s a solitary mansion, unremarkable in its traditional build if not for such a remote location.

The thing about most locations that serve as a demon’s base of operations is that those beasts lack the cognition to actually care for them. Overgrown, ruined, dilapidated, that’s how demon houses are. Not this mansion. While the greenery around it grows wildly and trees are so high they barely let the moonlight through, the house itself stands pristine.

“That’s a first,” Dio hums to himself, in no doubt that the demon haunting these woods actually resides here. He smirks, intrigued with what he sees. He decides that he’ll play a nice guest if that means an actual intelligent conversation with a fellow being that transcended humanity.

Companionship is scarce and precious, a mind unchallenged by another point of view is prone to degradation, and it’s been a while since Dio saw his so-called brother, to cut him with either barbs or knives.

In accordance with Japanese etiquette, Dio slides open the front door and steps into the entrance-way, no further than that.

“Please forgive me for bothering you.”

A second passes. Then two. Then Dio hears steps from within the plain-looking building. He’d prefer to decorate such a boring place with at least a few vases, though he won’t say that to his host’s face.

And then comes the said host, gripping the corner with a clawed hand.

To Dio’s surprise, the demon he sees might even be taller than himself. At the same time, despite the intelligence and cognition Dio deduced of the man, he might also be the most inhuman-looking demon seen by him so far.

The master of the house is a muscular man with grayish skin, long black hair and sharp black markings on his forehead. Blood-red sclera show no pupils. Most notable are the drums seemingly ingrained into his body, in his shoulders, on his hips, on his stomach. Most likely a part of his Blood Demon Art.

“I was hoping to find a sanctuary against the light of the coming day,” Dio says courteously as his cape billows behind him.

The two stand at a standstill.

“Hm. You’re… no human, and yet…” the demon murmurs, seemingly considering actually allowing Dio’s stay. “Something is off about you, you don’t feel like a regular demon, yet you are no Kizuki, too…”

“Dio Brando, a pleasure to make your acquaintance. And you…?”

Dio’s ease and confidence seem to take the demon off-guard as he blinks at the foreigner. Then he offers his own name in return, seemingly out of instinct rather than something conscious.

“...Kyogai.”

A pause. Then, Kyogai turns his back to Dio, revealing one more drum present there, between his shoulder blades, partly hidden with his long wild hair.

“You may stay…”

Kyogai ventures back into the depths of the mansion and Dio follows his host, curious about the demon, so quiet and reserved compared to the creature he’s seen before.

“You’re gracious to allow my stay.”

“Demons come and go…” Kyogai says quietly. “You’re the most polite one so far… Dio-san.”

It’s obvious Kyogai expects Dio to find a quiet corner to himself, but instead the man shadows the drum demon with a confident stride and the other doesn’t find it in himself to rebuff the man.

They two settle themselves in a room Dio suspects to be Kyogai’s study. Just like the rest of the mansion, it’s mostly empty, but this room in particular has a writing table with several shelves in it. It’s low, as is traditional, and Kyogai has to kneel to sit at it, shifting and deflating his form slightly to fit.

Dio is curious at the size-shifting ability, but he’s even more curious at the manuscripts inside the shelf Kyogai accidentally opens while looking for paper and writing utensils.

Almost unconsciously, Dio’s hand reaches for that shelf.

“May I?”

Red gaze pins down Dio’s hand but never stops him. Kyogai breathes heavily as Dio opens the shelf and carefully pulls out the written works. He can see the tension in Kyogai’s body. Despite his inhuman look, the vulnerability in his expression is so transparently human, so easy to bend to one’s will the foreign demon almost smiles.

However, Dio focuses on the writing first.

He’s not sure what he was expecting to see, but Kyogai’s writings turn out to be a poetry work, rhymes abundant, yet it’s structured like an epic, long and detailed, so Dio spends quite a bit parsing through it.

To his own surprise, he’s engrossed in the story about three warriors from the Heian period, protecting the peace of the lands when the Emperor’s forces were unable to. The point of view changes ever so often, yet seamless.

It’s… magnificent and refined.

His eyes just slightly widened, betraying his enjoyment, Dio looks at Kyogai, who’s Adam’s apple bobbles from how nervous the man is.

“Have you, perhaps, taken inspiration from Satomi Hakkenden?” Dio asks casually. “At first I thought of it as a coincidence, but with so many characters carrying similar names it has to be a reference, is it not?”

“It is… my favorite of classical works,” Kyogai replies shyly, yet there’s something like hope in his eyes. The guest at his home smiles at finally finding a worthy, refined conversation partner.

“Your artistic work truly is incredible,” Dio says, laying the manuscript carefully onto the writing table and Kyogai’s breath hitches at the verbal recognition of his talent.

Hook, line and sinker.

And yet, Dio feels like he’s not just manipulating an obviously insecure demon. He’s sincere in his praise, and while it’s to his benefit, he feels something more will come out of knowing his new… acquaintance.

Notes:

I can't believe I'm actually posting this thing when I have so many incomplete works.
But it's been in my table for a while and who knows, maybe I'll actually finish refining my kinda-old crossover outline into a befitting work.