My Vampire Older Sister and Zombie Little Sister

Chapter 0

[confidential] Concerning a Virus Known as Weather Report [storage A51]

This is a cyber-attack alert.

The hacker known as Maiden is active primarily within North American and Western European countries. The same individual or organization is thought to be classified as a “noble hacker” or “security tester” who uses their harmless virus, Weather Report, to spread an infection deep within the strict systems of governments and corporations, but we cannot predict when they will show their true colors and instead spread harmful ransomware or corporate blackmail.

This notification is addressed to everyone.

Change your passwords regularly, do not open suspicious email attachments, and be on the lookout for the telltale signs of spear phishing.

Also, both the CIA and NSA are tracking down Maiden, but we intend to deepen our cooperative relationship with the CIA. Keep that in mind when any disclosure of information requests arrive.

Chapter 0

“Hi, Truth. The days when you had to hole up in a dark room just because you’re a hacker are over. You should grab a smartphone or tablet and get some sun.”

I, Amatsu Satori, was sitting in a bedside chair as an awfully cheerful girl spoke to me over my smartphone.

The video blurred a lot, presumably because the footage was taken from the view of the pet robot sitting on her table. I was pretty sure that toy let you attach a handheld game system as the small dog’s head to handle its processing. Thanks to that, the focal point kept swinging all over the place and refused to settle down.

“Um, Anastasia?”

“It’s Maiden. Use my handle name.”

“Maiden. How old are you this year again? 10?”

“11! That’s completely different!”

The small girl on the screen wore a bewitching red camisole with a miniskirt as short as tennis wear and she also seemed to be angry. Annoyingly enough, the entire ensemble was silk.

Anyway, she seemed to be at an outdoor café, but…Americans really were something else. Urp. My stomach was close to raising the white flag after just looking at the mountain of fries and fried shrimp.

“So why is an 11-year-old hanging around Las Vegas on a weekday? Don’t you have school? Or is this just your country being as insane as ever?”

“Don’t give me that look after seeing just one measly pound of fries. And have you forgotten? This is the States where we say ‘freedom’ but mean ‘crazy’. Let the delightful sun wash over you and you’ll realize this is the best way to live your life. Why would I want to sit in an air-conditioned lecture room when I could be relaxing at a café and poking at the vulnerabilities in bank systems?”

…If she would keep her mouth shut, you might think she was a doll or a princess. She had almost transparently white skin, her long hair was a very light platinum blonde, and she had an Eastern European slenderness that…yes, it made her more “pretty” than “cute” even at only 11. But as soon as she did open her mouth, it was this.

Oh, and she used a very feminine form of Japanese, so she probably learned the language from manga since English doesn’t have male and female language.

“Um, Anastasia?”

“It’s Maiden! And I’m not listening to any lectures. All I’m doing is leaving a harmless test virus in the middle of the system as a kiiiind warning telling them to update their security. I am a righteous! White!! Hacker!!! The problem is with the government for using systems that can be penetrated by an individual hacker like me. I’ve even gotten into the control rod of a nuclear reactor and the military’s space division. Listen, I even got as far as Phase 2 in a Texas missile silo! If it wasn’t for the old-fashioned manual key, I could have launched it. If it had been a stealth bomber, I could have opened the bomb bay and dropped the payload. Heh hehhh!!”

She seemed to be happy, but did she keep going on and on about it because she felt guilty?

“Calling yourself a white hacker could be seen as racist, so be careful. I could see someone asking what that implied about a Hispanic hacker.”

She was a genius girl who had skipped grades to enter a certain Massachusetts university at her age. That land of the stars and stripes was a scary place because every classroom seemed to have one or two people who felt more like characters from a drama than real people.

Surprisingly, I had met this eccentric girl through online mahjong. I had been letting my disaster environment simulator named Maxwell play the game as a kind of benchmark test, but she saw through it right away. She said, “Chess and Reversi are one thing, but getting a program to play mahjong this well is impressive. What lab is this competition machine from?”

I had no way of knowing it at the time, but American researchers had been going all out to get machines to defeat all of the human masters of various board games. When Anastasia saw Maxwell “discarding tiles in a very lifelike and almost human way”, it had stimulated her curiosity.

By the way, Maxwell had not spoken for a while.

The reason why was obvious: If Maxwell said anything, Anastasia would start asking an endless stream of questions. Only counting the ones that came with an “official” announcement in advance, she had made 65 cyber attacks on us. She always claimed it was only to fulfill her academic curiosity in the field of data processing.

“Maiden. What if a third party finds your harmless virus and maliciously modifies it? That could lead to remote-control malware and ransomware that get in through the same route.”

“Uuh. I-if that happens, I’ll find the shameless bastard who stole my specialty and make them regret it. And if that leads to any false accusations, I’ll anonymously save anyone who was used as a stepping stone. No problem, see! Grr, grr!!”

And then the methods she used to take revenge and save people would be copied to give the other person more cards to play…but she’d just throw a fit if I said that. And I couldn’t deny that Maxwell’s firewall was being improved by this tiny hacker’s attempts.

“But anyway, they’re all completely insane,” said Anastasia. “The military, the power plants, the germ labs…everyone. Even if their main servers are fine, do you know what kind of terminals the workers use? They like to smugly call themselves experts, but they’re just carrying around normal bioroids inside fancy cases. Just because their corporate reception desk has a contract with a security company, they think their systems are impenetrable. And yet they’re no safer than you curled up at home watching porn on your tablet!!”

That said, she would never shut up if you directly thanked her either. I needed to approach from a different angle for this.

“Maiden. If you really want to call yourself a pro hacker, shouldn’t you stop revealing all this internal information to an outsider like me?”

“Hold on, master! That’s going too far!”

“I’m not your master! Stop calling me that!”

“But aren’t you the monster who single-handedly destroyed the Bright Cross!? And there was no money or fame involved; you were only fighting to free the weakened Archenemies. There’s no more perfect white hacker. Here in the States, people are saying that becoming Master Truth’s apprentice turns you into a hero who wields a glowing sword and destroys a space empire!”

“P-please no! I don’t need all that extra pressure…!”

“No matter what you think, Truth, you’re the all anyone’s talking about in our field. Do you have any idea how disappointing it would be to hear you’re not one of us!?”

This was bad.

I had no idea that was how people saw me.

“Then, um, does that mean what I think it does?”

“Yes. Some reckless but ambitious challenger might come knocking at any time. Hackers are like mountain climbers: when we see a towering wall, we want to climb to the top.”

Was she serious?

As long as I could make a detailed simulation of the Class Rep swimsuit dance file set, I had no further interest in the cyber field.

“Can’t you keep all that dangerous nonsense to yourselves? Why do crackers insist on getting outsiders involved?”

“Hackers!! We are solitary technicians!! Truth, you aren’t intentionally provoking me, are you!? Well, if you want a fight, just name the conditions! Choose a casino and we’ll see who can break through its defenses first!!”

“Okay, okay! You’re a genius, you’re a genius!”

Sheesh, before even talking about online security, she was shouting all this information in public. And in an open café no less. Even if she was just a kid and speaking to a handheld game system used as a head for a pet robot, were the other customers really that indifferent?

“Anyway, Truth, how about you get out more? The two of us can change the popular image of the pasty indoor hacker.”

“Sorry, but I’m not about to leave this air-conditioned room. Besides, the Class Rep is feeling sick for once, so I have to look after her.”

“Hmm. Biological bodies are such a pain. The cells are managed by a program, but we can’t control them properly because they use a different language. …Hm?”

Anastasia looked off to the side.

And that profile view froze in place.

She had stopped moving while looking at something.

“Hey, Maiden?”

I briefly panicked, thinking a police officer was questioning her.

But that wasn’t it.

Her widened eyes contained a purer and hopelessly uncontrollable fear.

“What…is that?”

“What’s the matter? Did something happen?”

I hated how cheap and generic I sounded. But the human mind refused to work with much flexibility when it really mattered.

And I heard something through the smartphone.

Cars honked and metal bent. Young men and women screamed and shouted. Something cut across the screen behind Anastasia. I had no idea what it had been originally, but it looked like a thick metal pipe that had been horribly mangled. And what else was that flying by? There were bagels, paper coffee cups, takeout bags, and lots of other odds and ends.

“Hey, Maiden, Anastasia! Listen!!”

“Eh? O-ohh.”

“Was it a traffic accident? An explosion??? No, you can explain later. Just keep your head low! Hide under the table!! You live in America, so you’re used to that, aren’t you!?”

It sounded like something from another world or from a movie, but this 11-year-old girl was all alone in Las Vegas, which meant she was on the front line of that gun culture. Things that seemed entirely bizarre in Japan could easily happen there.

But Anastasia herself seemed almost absentminded. She stayed in her chair, kept her head turned, and did not even try to move.

“Sorry, Truth…”

“For what!? Why are you apologizing!?”

“This has gone beyond a mere accident or crime. How am I even supposed to explain this?”


I couldn’t figure out what she was trying to say. She kept looking back and forth between something outside the screen and the lens of the handheld game system attached to the pet robot. She seemed unsure if she should show me what was happening before her eyes…

“Maiden, what is happening there?”


“Tell me, Maiden! Please!”

I could see her small lips trembling a bit in that profile view.

She seemed to be telling me not to regret this.

Then the camera blurred. She artlessly aimed it toward what she could see.

And my smartphone’s screen was filled with…translucent red slime.

The nightmarish vision showed that slime enveloping and digesting more and more passersby.

What was happening?

“They’re gels…” said Anastasia.

Even with this placed before my eyes, I wasn’t sure what to say. But these were definitely real deaths occurring there.

“Are they Archenemies?” she asked. “Regardless, these red gel monsters are eating people…”

Were they sulfuric acid? Hydrochloric acid? Nitric acid? Or something rarer like aqua regia or hydrofluoric acid???

They were about the size of a puddle that you would need a running start to jump over. Was it even possible to make a human body dissolve that cleanly if you dumped a bucket of highly-concentrated acid on them? Even those XL-sized Americans were gone in less than twenty seconds! Not even their hair or bones remained!

And being dissolved by acid while alive was too bizarre a way to die. What kind of life would you have to live to meet a fate like that?


Even so.

There wasn’t time to avoid the reality on my smartphone screen. In a distant Vegas café, red slimes large enough to swallow adults whole were crawling around and doing more and more damage. At this rate, Anastasia would be surrounded and lose any chance of escaping.

And then I would have to see an 11-year-old girl dissolved until not even her bones remained.


“It’s…Maiden. Wh-what is it?”

I breathed in and out.

At the moment, my smartphone could act as a weapon to help her cross that battlefield.

It would help her escape those unidentified Archenemy Gels.

It would help me protect this distant friend.

“Maxwell and I will give you our full support. So make sure you get out of there alive!!”

[confidential] Concerning Las Vegas [storage A51]

An important tourist resource in Nevada and a world-renowned casino and theatre city. Access via land routes is possible, but as it is surrounded by a harsh natural desert, most people rely on McCarran International Airport.

The guest population is estimated at about four million.

Development is primarily focused on the main street which is lovingly known as the Strip. Development is especially fierce and land prices especially high at the intersections known as the Four Corners and the New Four Corners.

Given its location, personnel at this air base frequently visit the city, so we must be careful to avoid accidents or information leaks while intoxicated. We must be especially concerned about soldiers’ interactions with moneylenders or prostitutes.

All personnel visiting the city must provide a detailed observation report and avoid carrying small spy tools like those seen in movies. Reports of casino security detaining them on suspicions of cheating sound silly, but it happens quite frequently. It will take even longer to ensure the release of anyone who is falsifying their identity, so keep that in mind.

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Volume 4