V-Killer's Pros, Cons, and the Red Cross Disc

It looked like a lawsuit from the Red Cross was about to come flying in thanks to the new weapon. “First, let me organize the pros and cons of V-Killer...” Moon Naru began typing out a list of V-Killer's strengths and weaknesses on her smartphone.

She added annotations to the pros and cons and mulled over how to address them.

• Stronger attack power than most pure offensive robots

└ Let’s add a single blade.

The fewer blades there were, the heavier each individual one became, which increased its power. The downside was that a single hit would bleed off a lot of kinetic energy. Because it lost so much rotational speed, it naturally needed a longer reacceleration time.

“Ugh… when am I supposed to design the single blade?”

• Narrow attack range for a horizontal spinner

└ This one can’t be fixed no matter what! !@#$% There’s no way I can overhaul the chassis from the ground up.

“Ah… this is the kind of problem you can only solve by tearing the entire robot apart from its foundation.”

• Defense exceeding that of most defenders

└ Add a lower protective ‍‍‌‌⁠​​⁠‌​​‍​​‍​‌​⁠‍‌‍⁠⁠‌⁠‌‍‌‍‌‌‌‍⁠​‌​‌​‌‍‌‌‌⁠‍​​‌‍⁠‌‌⁠⁠skirt. “Let’s try putting a skirt on it. It’ll probably look a little weird, though…”

It was a spring-loaded skirt designed so opponents couldn’t easily dig underneath. But because the robot’s ground clearance was so high, the shape came out extremely bizarre. It didn’t look like a sporty miniskirt at all. It ended up resembling a medieval dress.

“A disc is more stable than a blade, right? Should I throw a disc in too?”

A disc was roughly a circular plate with attack blades mounted on it. Its disadvantages were weaker impact than a blade and slower acceleration. On the other hand, once it got up to speed it didn’t stop easily and had less recoil.

“What shape should I go with… Oh, Red Cross!”

The origin of V-Killer—‘Virus Killer’—flashed through Naru’s mind.

“That’s it. A four-blade disc! Aluminum cross in the center, steel square frame around it!”

To put the thought process simply: virus extermination → doctor → Red Cross → cross-shaped weapon → four-blade disc. And why aluminum in the center with a steel rim? It made the middle light and the outer edge heavy. Centrifugal force would increase, boosting the attack power.

“Okay… let’s build it like this!”

Leaving only the ideas written down, Moon Naru headed off to wash up.

“It’s my body, it’s my body… I don’t need to think weird thoughts!”

She still had to look at that scene again, so embarrassment washed over her.

“When am I ever going to get used to this…?”

After forcing herself through the shower, she fell asleep immediately.

When she woke up, it was already Friday morning. Just one more day of school and then the weekend. The moment she arrived on campus, Moon Naru received an anonymous letter.

“Naru, they said there’s a letter for you.”

“Who sent it?”

“They told me not to say. It should be written inside, right?”

The moment she realized it was a painfully cringy love letter, Moon Naru immediately looked for the sender’s name at the very bottom.

“Lee Ji-soo, second-year class six.”

(After everything, I’m receiving a love letter from a girl while in a girl’s body.)

(There’s no way Ji-soo is a lesbian.)

She had once witnessed Ji-soo confessing to a male student. Back when Naru had still been a boy.

(If she’s not a lesbian, then is she bi…? That feels weird too.)

She set aside the burdensome attention that continued today and headed home.

Fi-na-lly! She fired up the design program, CAD.

“Ugh… designing a single blade is ridiculously hard…”

If the center of mass didn’t line up with the axis of rotation, the farther off it was, the stronger the vibration. It perfectly matched the operating principle of a vibration device.

(When am I going to finish matching all these centers of mass…)

On top of that, it was an asymmetrical weapon with a blade on only one side. The process of aligning that center of mass to the rotation axis? You had to tweak it piece by piece until it matched. Naturally, it was insanely tedious. What if she left it to an AI? She’d need one specialized for the task. She wasn’t sure if one even existed.

All Friday evening, Naru worked solely on matching the center of mass.

“Kyaaaaah! I got them all matched!”

She had finally aligned the troublesome centers of mass. In her joy she let out another pterodactyl-like shriek.

(It’s not perfectly accurate, but since machining can fix it!)

The rest of the weapons were symmetrical, so they were finished quickly.

“This looks way too much like an actual Red Cross… what if I get sued?”

The Red Cross emblem was restricted under the Geneva Conventions. Using it incorrectly could be illegal, so one had to be careful.

“Would the Red Cross really bother caring about an amateur battle robot tournament?”

Before she knew it the time was already eleven. After brushing her teeth, washing her face, and rinsing her feet, Moon Naru went straight to bed. It was quite late, and the thought of seeing that scene again felt too burdensome.

“Tomorrow’s the weekend, but… I still need to sleep.”

The next day, the moment she woke up Naru logged into the metal fabrication company’s website.

“Aluminum 6061, and for steel… let’s go with this one.”

Both were metals she knew all too well. Friendly names you could see anywhere in daily life.

“How many metals can actually beat steel?”

Iron was a metal with history and tradition stretching back to prehistoric times. At first it had been used simply because it was cheap, but technological advances had gradually made it stronger.

“Steel isn’t just for being cheap and tough~!”

It carried the image of a ‘cost-effective material’ used purely for that cheap-and-tough appeal. Fantasy games often portrayed it the same way.

“Titanium is only strong in fantasy games.”

In reality, there weren’t many materials that could absolutely outperform iron. Titanium was used for its strength-to-weight ratio, and it wasn’t all that light either.

“The center of mass isn’t perfectly aligned, but it’s waterjet anyway! Cutting knives with water!”

Waterjet machining was essentially the principle of “raindrops piercing stone” sped up ten-thousandfold. The opposite of “cutting water with a blade,” it was a method that allowed “cutting a blade with water.” It sliced material by firing water at tremendous pressure. When cutting hard substances, abrasives were mixed in. The advantage was natural cooling; the disadvantage was that precision was basically nonexistent. Of course, for everyday purposes it was considered fairly precise. From a pure engineering standpoint, however, it had no precision at all. ‍‍‌‌⁠​​⁠‌​​‍​​‍​‌​⁠‍‌‍⁠⁠‌⁠‌‍‌‍‌‌‌‍⁠​‌​‌​‌‍‌‌‌⁠‍​​‌‍⁠‌‌⁠⁠Expecting accuracy when cutting with water was strange in itself.

“Laser or waterjet, neither one has real precision!”

Laser machining was practically the same story when it came to engineering-grade accuracy.

“The processed parts are scheduled to arrive… on August 31st.”

They would arrive at a perfect time. The first day of the national tournament was September 2nd. Once the parts arrived and the post-processing was finished, they could be used right away in the national competition.

“Until the parts get here I’ll do some exhibition matches and watch RCLK too~!”

RCLK (Robot Combat League Korea). South Korea’s premier professional battle robot league. It was one of the six major leagues alongside Europe’s ERFL, India’s IRFC, China’s CRCL, Northern Europe’s NFRC, and America’s NARC.

“I’ve been watching since I was little. I never imagined it would get this popular!”

Naru was a longtime fan of RCLK. She had followed it since the very first season in 2018 when it had launched as a semi-major league.

“Back then it was questionable whether they could even sell out four hundred and fifty seats. Now they’re selling out seven thousand?”

(I’ll be competing there soon too…!)

Before she knew it, August 31st had arrived and the machined parts were delivered.

“Red Cross disc, large single blade, small single blade, three-blade disc, spring skirt. Everything’s here!”

Naru didn’t need to do any extra work like welding. Everything was designed to be assembled with screws. Since the parts would break countless times during matches, they had to be easy to repair.

“Let’s start with testing. Small single blade first!”

She began testing with the single-blade weapon that required separate center-of-mass tuning.

“If I detach just the weapon drive unit and slot it in…!”

“As expected, it vibrates a little. Let’s grind this section down a bit.”

As mentioned before, waterjet machining had virtually no engineering precision. After shaving a tiny amount off the heavier side, the vibration vanished like magic.

“The large single blade… somehow the weight is perfect?”

She had gotten lucky; the center of mass matched exactly. It was like hitting third prize in the lottery.

“Now assemble the Red Cross and three-blade, center and rim together…”

Because the center was aluminum to optimize centrifugal force, it needed to be assembled. Since replacements might be necessary later, it was screwed together.

“This one fits perfectly! It’s symmetric, so of course it does.”

With rotational symmetry, the center of mass rarely shifted.

“Now I just need to paint it and let it dry.”

“I should wear a full gas mask instead of a KF94.”

A KF94 could block virus-laden droplets, but its filter structure couldn’t stop the toxic fumes from paint.

By the time the paint dried, the national tournament would be starting.

“Let’s post this on SNS too. ‘In the middle of making new weapons…’”

Drawn in by Moon Naru’s appearance, an enormous flood of comments poured in.