My Vampire Older Sister and Zombie Little Sister

Chapter 0

Part 1

[Pick up] Multiple IC Student IDs [Net files]

Amatsu Satori

15, Male

Public Kukyou 1st High School (General Education)

First Year


Amatsu Erika

17, Female

Public Kukyou First High School (Night Division – Special College Prep)

Second Year

※Archenemy “Vampire”

Amatsu Ayumi

14, Female

Private Elixir Girls Middle School (Vocal Music Scholarship)

※Archenemy “Zombie”

Part 2

[Pick up] Local Net Radio Opening [Net files]

Okay, okay! Tonight’s Brand New Stars begins!!

The wind is still blowing like crazy out there, so I’m guessing there’s a lot of you holed up your cheap hotel rooms wishing you hadn’t chosen today to do some sightseeing!

But this awful weather is what it’s all about! Make sure you get a good taste.

Here in Kukyou City, we’ve always had a lot of natural disasters. The cold wind blowing down from the mountains to the west collides with the damp air on the coastline to the east, creating a ton of instability, so we’re especially well known for our tornadoes and lightning strikes. But our greedy spirits are always going to find a way to benefit from bad news! Prestigious universities are lining up to send research teams to understand the complex mechanism behind various disasters in the hopes of predicting them in advance. They’re also building technology to reduce the damage done. Shocked, aren’t you?

We aren’t known as the Disaster Protection City for nothing. We’ve got doors like bank vaults below each house and metal-walled tornado shelters to protect our residents when it matters. If you check with the firefighting hoses stored here and there along the roads, you’ll also find rubber boats in case of flooding. And get this! They use the power of carbon dioxide gas to inflate like an airbag!!

In other parts of the city, we have special bundles of sensors known as Weather Spheres and backup power systems just in case. Kukyou City is full of experimental things like that, so anyone into survival or outdoorsy stuff will be salivating at all the things they see around town.

In the near future, the disaster prevention and protection systems developed here might just find their way to your cities.

And maybe you think the name Kukyou City is a little ominous. It sounds just like the word for crisis, so you’d expect to see it in a closed-room murder mystery, right!? But it’s not like anything ever happens at the Tenryu River or at the Yashajin Pass and the locals really aren’t bothered by it.

Oh, the intro’s starting.

Now, now. Let’s get the first song going! This one’s known for being the ending theme to Feast of the Undead, that gory movie opening this week!

Part 3

“If a zombie and vampire went all out, which one would win?”

That topic came up after I took my bath.

I think everyone naturally wants to mess with their phone after getting out of the bath. A ton of pointless SNS messages like “eating dinner” or “on a walk” will pour in and the new messages pile up in the short time since you last checked. And everyone will get upset if you don’t respond, so you can’t take it too lightly.

But things were a little different that day.

My younger sister Ayumi had taken a bath before me and she was lying on the living room sofa with a popsicle in one hand.

“Your smartphone’s been buzzing up there on the table. It sounded like an incoming call.”


I looked away from her face as I gave my brief answer. She was in middle school and, um, how should I put it? I was having trouble figuring out where to look. Her black bangs were cut straight across and she had long twintails that spiraled at the very end. Her flat but growing body was covered by a thin camisole and shorts, so just lying there was enough to see her somewhat flushed belly and similarly flushed thighs just about up to the base.

However, her face, belly, arms, legs, and pretty much everywhere were covered in stiches like a poorly-made stuffed animal.

This was not because she was fighting some serious disease.

She just happened to a bit of a zombie.

“Oh, honestly! It’s hot! So hot! I dried myself off so very, very thoroughly, but I’m still sticky all over. I’m gonna rot. My body’s gonna rot!!”

“Throwing a tantrum isn’t going to change the one-popsicle-a-day rule.”

“Then fan me, Onii-chan! One fan isn’t enough! I need more manpower!!”

She shoved a fan into my hands while still lying on the sofa, but that presented something of a problem. Her camisole was pretty baggy, so I could just about see her modest breasts down the neck.

“Besides, if you’re itchy, you should use your preservative. Isn’t your body temperature supposed to drop when you cool that and give yourself an IV?”


For some reason, she pouted her lips between her twintails that had ringlet curl tips (which I thought looked like dinner rolls).

Meanwhile, the person elegantly lounging on the opposite sofa cut in with a grin on her lips.

“You’re missing the point. Ayumi-chan just wants to indulge in her Satori-kun a little longer. Isn’t that right?”

“N-no!! It really is just too hot to bear!!”

My older sister Erika’s smile remained intact when Ayumi yelled at her.

She was a sexy girl with waist-length blonde hair in splendid ringlet curls. She had gentle eyes and was a year above me in school. However, I had an inkling that Ayumi wouldn’t turn out like this even after a few more years of growth.

That said, my older sister gave me just as much trouble figuring out where to look. I wasn’t sure if it was supposed to be pajamas or underwear, but she wore a light pink negligee that was see-through enough to make out the skin below it.

She was so perfect I had to wonder why she wasn’t the student council president. She was almost flawless if you ignored her obsession with cleanliness and how long she spent in the bath. Not that I was sure I would call Ayumi’s excessively short baths a positive trait.

“Onee-chan, what are you doing over there?”

“Mom and dad can’t get home because the trains were shut down due to the strong winds, remember? I’m sitting here waiting impatiently for a chance to use these disaster goods☆”

The table was covered in a pile of canned food, candles, portable radios, helmets, and bundles of rope. Although the cans were all pineapples and white peaches, so I wasn’t sure we could live all that long on just that.

“I really doubt the power will go out. I mean, this is Kukyou City, right?”

“Eh heh heh. But, but. Why is the thought so exciting?”

“Onee-chan, if you’re really worried about a blackout, shouldn’t you start by moving the contents of the fridge to a cooler?” asked Ayumi while munching on the vanilla popsicle that had started to melt. “You’d be in trouble if your blood and substitute plasma went bad, right?”

Oh, that might sound concerning, but it isn’t anything too heavy.

This was not because Erika was fighting some serious disease.

She just happened to be a bit of a vampire.


Not even I knew how this had happened.

Those two became my new sisters when my dad suddenly got remarried, but Ayumi was already a zombie and Erika was already a vampire by then.

There’s probably some detailed explanation that would fill up about 400 pages when written out, but that doesn’t matter here. As long as we got along, they weren’t going to take a bite out of me.

My negligee-wearing older sister gave a gentle comment.

“More importantly. Satori-kun? Ayumi-chan was right about your phone buzzing. Shouldn’t you call whoever it was back?”

“Oh, that’s right. Excuse me a moment.”

I grabbed my smartphone from the table and walked to the kitchen located across from the living room. I checked the call history and touched the most recent one to redial. Soon, a familiar voice reached my ear.

“Sorry. Were you busy with something else?”

“No, you’re good. More importantly, what do you want, Class Rep?”

“It’s about tomorrow.”

The girl I was speaking to was actually our neighbor. She was a childhood friend of mine known for her forehead and glasses. Unlike Erika and Ayumi, she was a normal human.

“With this wind, odds are school will be canceled tomorrow, but you still have to do your homework just in case. Even if you come crying to me after waking up to find a clear blue sky, I’m not letting you see my notes.”


“And even if school is canceled, you can’t waste the day having fun. Since you won’t have the teachers around to manage your time for you, you’ll have to work even harder to study on your own.”

“Oh, god. I can’t believe this Forehead Glasses Class Rep.”

“What was that!?”

I heard the yell from outside the window, not the phone.

In fact, the neighbor’s window burst open so a face with prominent forehead and glasses could yell at me with the look of a wild beast.

“I thought you swore to never call me that again back in sixth gra- dwah!? Th-the wind! It’s whipping at me even indoors!!”

“I’m more interested in why you’re in a bath towel! Your phone has a camera on it, so taking it in the bath with you is a bad idea!!”

“How is that impor-…hyah!?”

“And way to go, Class Rep!! You don’t even take off the glasses in the bath, huh!?”

“Stop! Making! Fun! Of! Me!!”

The Class Rap was badly beaten in the first round of the North Wind and the Sun, but she just barely managed to grab at the edge of the towel and hold it in place.

“Pant, pant… A-about the glasses. I need them to tell the shampoo from the conditioner. Anyway, what are we going to do if school is canceled tomorrow? Should I head over there to help you study?”

“Even if you’re just next door, this wind and rain would destroy your umbrella and you’d be left soaking wet. I have Ayumi and Erika, so I’ll be fine.”

“…Personally, I think those unbelievable sisters are the main problem.”

She muttered something under her breath before speaking to me again.

“Well, just keep up your steady pace like you do at school and anything else is fine.”

“What will you be doing tomorrow?”

“Watching some movies.”

Wait. What happened to studying?

“When I was cleaning my room, I found a few I’d never gotten around to watching after renting them online. The company I used doesn’t charge late fees, but I have trouble working on anything else when I leave a task undone.”

“Hm. Knowing your tastes, I bet I know what genre they’re from.”

“(Those aren’t my tastes. It’s to go along with you three.)”


“Nothing. And yes. They’re all ones with zombies, vampires, axe murderers, and mysterious slime aliens. Oh, and I think there’s one about a showdown between two different monsters.”


It was supposed to be a casual chat.

I didn’t meant anything by it.

The thought just so happened to occur to me based on what the Forehead Glasses Class Rep said.

“If a zombie and vampire went all out, which one would win?”

I hadn’t noticed.

I hadn’t noticed the gravity of what I was saying.

And I couldn’t deny part of that had to be with how much of my mind was focused on the Class Rep’s sexy body barely covered by the bath towel.

“Wouldn’t you know better than anyone, Satori-kun? You’ve seen them both up close.”

“Yeah, but I’ve never seen those two get into a real fight with hair grabbing and stuff. They’ll argue over who gets the last popsicle, though.”

“I wonder how it would turn out for real?”

“Yeah, they both have supernatural strength and can increase their numbers by biting people.”

Two presences may have been slowly approaching behind me, but I didn’t notice at all.

I never would have imagined how this would turn out.

“It may seem like apples and oranges, but it might end almost too quickly once it starts,” I said. “Y’know, like when they have the ‘Judo vs. Karate Match of the Century!’ and then it ends after a single round and everyone’s disappointed.”

“Ah ha ha. Maybe so. …Um, well, everyone has their own opinions on these things, so I can’t say anything for sure.”

“Hm? What’s wrong, Class Rep? Why are you ending that topic so suddenly?”

“Ha ha ha ha ha. Okay, I think I’m going to hang up. Satori-kun, I don’t care what happens to you tonight. There’s no excuse for not studying tomorrow, okay?”


The call ended.

Immediately, intense strength grabbed both my shoulders.

I was spun around, but…

“Ow, ow, ow, ow!! If Ayumi spins me to the right and Nee-san spins me to the left, I’m not going to spin either way! Are you trying to tear me in half?”



They must have known competing over this would get them nowhere because both sisters circled around in front of me.

Their smiles were frightening.

I could almost see the dark shadows falling on their faces.

“Satori-kun, about what you were talking about…”

“Wh-what I was talking about?”

“That’s right, Onii-chan. About whether a zombie or vampire would win in a fight.”


Oh, crap. This isn’t heading anywhere good.

I finally found – no, captured – my sense of danger as those two girls’ faces moved disturbingly close to mine with beaming smiles.

“The zombie would obviously win.”

“The vampire would clearly win, wouldn’t she?”

Their sweet-smelling voices were in perfect unison.

That was exactly what I would expect from those two who kept their ringlet curls even in the bath. And if they were so perfectly in synch here, couldn’t they please stop fighting!?

“That look! You don’t believe me, Onii-chan!!”

“Satori-kun, you think a vampire is a sickly nocturnal human who turns to ash in the sunlight, don’t you?”

They spoke at the same time, but this time there was no harmony and sparks flew as their gazes clashed.

“Then how about we test it out?”

“Yes, let’s show him which one is the true Queen of the Night.”

“Pff. Queen of the Night!? What’s with you vampires? You’re like the embodiment of cringe.”

“I don’t want to hear that from a rotting second year in middle school. And are you trying to say zombies are at the top!? Pfa ha ha. Are you referring to the zombies that get one-shotted by anything with the ‘holy’ attribute? Or maybe those poor kids who are the only one that gets damaged by the healing magic? Ha ha ha ha.”

“Why you…!!”

“You got a problem with that!?”

The camisole + shorts and the see-through negligee got into a scuffle. I really didn’t know where to look. In fact, while I would stubbornly refuse to admit it if they asked, I was pretty sure I could see some things. No, I could pretty clearly see a number of things.

Wow. So that’s what a girl’s body is like there.

I wasn’t sure what to do and ended up nervously standing there and staring, but my sisters ignored me and gasped for breath as they argued at point-blank range.

“Oh, honestly! This isn’t going to get us anywhere!!”

“Agreed. Besides, our true value is in amassing pawns, not individual fistfights. It’s all about the horror as we see who can acquire more people and fill up the city first! We could never settle this in a one-on-one fight!!”

“Then are we gonna do it!?”

“You said it first! Don’t blame me when you regret those words!!”

What were they planning?

Ayumi and Erika continued ignoring me as they made a simultaneous announcement.

“We’ll start a pandemic in Kukyou City! Who will conquer the city first, the zombies or the vampires!?”



Wait, wait, wait, wait!! Hold the phone!!

What did those monsters just say!?

“Y-you can’t do that!! What kind of idiot destroys an entire city over a fight between sisters!? And it won’t just be cute girls turning into vampires and zombies. Who wants some greasy old man zombie!? Are you sure you want to deal with that!?”

“That’s not what we meant.”

My negligee-wearing sister turned toward me and waved a hand my way.

“Satori-kun, you have that environment simulator you made, right? Can we borrow that?”

“That thing completely recreates Kukyou City in virtual reality, right? We can safely spread all the horror we want as we bite at the people realistically running around, right? Let us use that, Onii-chan.”

“I’d rather not!! That’s meant to simulate the damage done by earthquakes and tornados, determine where the congestion occurs as the panicked people try to flee, and figure out how to get everyone to safety. It isn’t meant for some cruel FPS like that!”



The air seemed to grow sticky.

Why did they both give me a sidelong glance in perfect unison when they were supposed to be fighting?

And Ayumi took the first shot with the ends of her twin tails curled around like dinner rolls.

“Are you trying to say alien invasions and wars between giant robots are serious scenarios?”


“That must mean secretly borrowing a detailed 3D model of the Class Rep next door and having her do a seductive dance in a risqué swimsuit is the proper way to use it☆”


How do they know about that!?

Th-th-th-the Sexy Class Rep Dance File Set’s folder was supposed to be stored where no one would ever find it!!

“Well, I’m sure any boy would want to see their serious and strict Forehead Glasses Class Rep shaking her hips more than a reggae dancer.”

“But I’m betting that Class Rep wouldn’t just almost kill him if she found out. Right, Onii-chan? We might end up with one of those ‘humans were the most frightening monster of all’ endings.”

Tremble, tremble, tremble, tremble, tremble, tremble, tremble, tremble, tremble!!

“So. If you lend us the key to the simulator, no one has to see that downer of an ending.”

“That thing’s meant to simulate natural disasters, right? Then it’s probably built to handle crazy parameters like this!! Zombie vs. vampire! Who will survive to the end!? Sounds like a fun theme, right, right, right!?”

There was nothing I could do.

I tearfully handed over the USB hardware key hanging from my neck.

That completed the preparations for the showdown of the century.

Ayumi and Erika both grabbed devices that looked like wireless headphones.

They were mind input devices. They were meant to let you experience a fictional disaster (or a Class Rep’s swimsuit dance) by linking you to my environment simulator named Maxwell, but rather than provide alternative input for your senses, its data provided you with the dream you wanted.

Heading back to their rooms must have been too much work because they lay down in the opposing sofas.

“Okay, you be the judge, Onii-chan. Use your god’s-eye-view to monitor the data from outside.”

“Eh heh heh. Satori-kun, I’m willing to overlook a bit of mischief, but in the interest of cleanliness, try not to get my hair or clothes dirty.”

As soon as they put the headphone-style devices on and flipped the switch by the ear, the girls lost consciousness like they had been unplugged from the wall.

“Oh, honestly.”

Once the commotion ended, the roaring wind seemed to grow much louder.

There was nothing for me to do there, so I decided to do as my little sister said and judge their virtual fight using the monitor in my room. For a touch of revenge, I stopped by the fridge to borrow the treasured pudding they had been looking forward to and I walked down the hallway with a spoon in my mouth.

The stairs led up to the bedrooms on the second floor and down to the basement.

But that basement did not hold Disaster Environment Simulator Maxwell. It was the entrance to the tornado shelter that every house had in Kukyou City. The door was as round and thick as a bank vault door. It had excited me when I was little, but I had never actually had a chance to open it.

I climbed the stairs to my room.

I placed the pudding on the study desk, tapped at the computer in sleep mode, and then got a call on my smartphone.

However, it was not from a classmate or my childhood friend the Forehead Glasses Class Rep.

“What is it, Maxwell?”

The simulator with its own SNS account displayed a message in a speech bubble.

“I have a concern related to a task labeled high priority.”

“Be more specific.”

The disaster environment simulator was made for realistic scenarios, so it may not have been able to handle a direct showdown between a zombie and a vampire. I could only guess that it had hung up when an error occurred somewhere.

But that was not the case.

Maxwell made another post.

“This is related to the Class Rep Swimsuit Dance File Set which was set at maximum secrecy.”


“If she dies during a simulation, the data will automatically be sent to the related organizations in order to put together countermeasures toward her cause of death.”


“So if the Swimsuit Class Rep falls victim to the current zombie and vampire simulation, the file set you have kept hidden may be exposed to the outside world. What should I do about that?”

“Crap, crap, crap, crap, crap, crap!! Craaaaap!! Anything but thaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaat!!”

I tore at my hair.

I wasn’t going to let some old men I’d never met learn about and mock me for my fetish! That was worse than being a fish on the chopping block!!

I quickly moved my fingers to my computer, which was a remote control terminal for the simulation.


“Maxwell, explain to me why my cancel simulation commands are being rejected!!”

“Sure. Amatsu Erika and Amatsu Ayumi have both logged in with administrator privileges, so their privileges are equal to your own. I can also speculate that their extraordinary parameters as a vampire and zombie are applying pressure to the entire system, creating too much chaos for outside commands to be accepted.”


“You cannot forcibly cancel the simulation.”

“I can’t believe this!” I shouted while pulling a headphones-like mind input device from a drawer.

The virtual city would soon be overrun by zombies and vampires. If the Swimsuit Class Rep fell victim to that, my social life was truly over. Not only would those old men with formal titles like “professor” be mocking me, but who knows what would happen to me if the Forehead Glasses Class Rep herself learned about the Swimsuit Dance File Set. Iron fist…elbow…oh, and I was pretty sure she had earned 2nd Dan in kendo. I was truly hoping she wouldn’t actually use a wooden sword on me.

That left only one thing to do.

“Maxwell, you don’t have to think about taking back my privileges. Can you slip me into the running simulation as a normal user?”

“Sure. But as a normal user has fewer privileges than an administrator, you will be able to participate, but you will be at a considerable disadvantage. For example, you cannot do anything related to ending the simulation, so you cannot end your participation on your own. You will be forced to continue on until the ending the administrator has in mind.”

In this case, that would be a definitive conclusion in the zombie vs. vampire showdown.

Whichever one won, the virtual city would have sunk into an ocean of blood.

I could not take this lightly just because it was virtual reality.

It was exactly the same as the city we lived in every day. Just like with an earthquake or a tornado, I would have to watch until the very, very end as the city was destroyed by a zombie and vampire.

This was a disaster environment simulator.

The parameters were a little out of the ordinary, but it would still fulfill its proper purpose.

“I’m still doing this. It’s better than being killed by the Class Rep in reality. Maxwell, prepare to log me in. I’ll head on in as soon as that’s done.”

“Sure. Rewriting certain privileges. Reregistering you as a normal user.”

My goal was clear.

As the zombie and vampire went on a rampage and created more rampaging monsters as secondary and tertiary damage, I had to do whatever it took to protect the Swimsuit Forehead Glasses Class Rep until it was all over.

Now, allow me to repeat the fundamental question once more:

If a zombie and vampire went all out, which one would win?

Part 4

[Pick up] Today’s Blog, Report of Completion. [Net files]

Tah dah!

I’ve been writing about the production of Maxwell for a while now, but it’s finally complete!!

Even I was worried whether an individual could really make an environment simulator, but I’m glad I somehow pulled it off.

Maxwell’s core unit is made up of the VS-Life 3D handheld game systems that went on sale just the other day. Yes, the ones that were recalled after the initial lot started giving people electric shocks. Due to the retail network, the used shops couldn’t send them directly back to the manufacturer. Since they couldn’t sell them, I managed to buy up a bunch of them dirt cheap, opened them up, and parallelized the processors.

But securing the processing power wasn’t the biggest problem. That award goes to the cooling system and power supply (mainly the transformer part).

Maxwell’s main body fills up about a single storage container, but I needed another whole container for those two things.

And Kukyou City really is a unique place. While I had to put it together all on my own, a bunch of people helped me as I tried to build this disaster environment simulator. I doubt universities and research labs would normally just reveal the management flow for their parallel machines. We just think about disaster prevention and protection differently. Then again, I do have to supply the simulation results to the various research labs to repay them!

Maxwell is made by hooking together about 1400 of the processors from those new systems, but they’re all working pretty well. It’s going great. When I put in the parameters for a typhoon or wildfire, it shows me where the people gather and where the congestion is in the fictional city. Oh, and this simulator doesn’t need you to model the residents. It uses the small traces left in the buildings, equipment, resource consumption, and energy consumption to determine where people have to be and builds up the human data that way. What an age we live in.

My next task is figuring out how to put all this processing power to use.

Namely, I need an interface.

There are a few mind input devices on the market, so maybe linking to the simulation with those can let you see how the people flee during a realistic disaster. I have a feeling that would be good for preparedness training.

Part 5

[Pick up] Parameter Adjustment Handwritten Notes File [Net files]

Memo memo.

Vampire. ← Nee-chan. Cowtits.

Part 6

Zombie. Idiot. Flat chest. ← No, that isn’t a compliment.

Not much to write for this one. ← There isn’t much to you zombies, is there?

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