The Yandere villainess loves the useless engineer

The next two weeks passed in a blur of steam, metal, and frustration.

I spent almost every waking hour inside the shack trying to improve the steam car while Finn slowly lost faith in both engineering and life itself.

The machine worked.

That was no longer the problem.

The problem was that it worked badly.

The suspension still rattled violently over rough terrain, the steering occasionally locked during sharper turns, and the boiler leaked steam from nearly every major connection point no matter how many times Leon refined the fittings.

Every improvement simply revealed three more flaws.

By the third day I had already rebuilt parts of the suspension system entirely.

The original leaf springs were too stiff, causing the entire frame to violently shake whenever the wheels struck uneven terrain. But I had eventually solved part of the issue by layering thinner steel strips together instead of using fewer thick ones.

The change immediately improved ride quality.

Slightly.

Finn still looked like he had survived a natural disaster every time they tested the vehicle.

"This thing hates the human spine."

"It’s better than before."

"Before I thought death was guaranteed. Now I think permanent injury is guaranteed."

I just ignored him while tightening another bolt beneath the chassis.

The workshop itself slowly transformed into a graveyard of failed components.

Steam leakage remained the worst issue by far.

No matter how carefully I machined the metal parts, pressure escaped constantly through microscopic gaps between joints and moving components.

The current seals simply weren’t good enough. 𝗳𝐫𝚎𝗲𝚠𝚎𝗯𝕟𝐨𝘃𝚎𝗹.𝗰𝗼𝗺

The higher I pushed the boiler pressure, the worse the problem became for me.

And I needed higher pressure.

Without proper sealing, the entire future of steam technology stalled.

Which was why I spent almost every evening thinking about the strange white sap Cedric mentioned.

The idea kept growing inside his head.

Elastic material.

Flexible seals.

Heat-resistant padding.

Shock absorption.

The possibilities felt endless.

One afternoon, while I lay halfway beneath the steam car adjusting part of the steering linkage, Finn suddenly looked out the workshop window.

"...We’ve got company."

I just slid myself back out before wiping grease from his hands.

A carriage slowly approached the shack clearing before coming to a stop nearby.

Then Cedric Ross stepped out.

The merchant representative still looked irritatingly clean despite traveling through forest roads.

Dark formal clothing.

Perfectly styled hair.

Not a single trace of soot or oil anywhere.

Leon genuinely wondered if the man slept inside a bath of perfume and money.

Cedric glanced around the workshop clearing before his eyes landed on the steam car.

For several moments he simply stared at it silently.

"...Every time I visit this place I feel less safe."

"That’s because you’re intelligent."

Cedric sighed softly before stepping closer.

"I’ve acquired the substance you requested."

My attention sharpened instantly.

"You found it?"

Cedric reached into the carriage before removing a wrapped bundle roughly the size of a loaf of bread.

The moment I took it, he immediately noticed the texture.

Flexible.

Slightly sticky.

Elastic.

Even untreated, it stretched slightly beneath pressure before slowly returning to shape.

My eyes widened faintly.

Rubber.

Or close enough.

Finn leaned closer curiously.

"...That’s the magical tree slime?"

"It’s latex."

"That word still means nothing to me."

Cedric folded his arms calmly.

"The material comes from a hotter southern region far beyond the main trade routes."

I could barely heard him anymore.

My fingers pressed against the material repeatedly while my mind raced through possibilities.

Pipe seals.

Pressure gaskets.

Flexible tubing.

Wheel padding.

Steam insulation.

Belts.

Industrial machinery.

Dear god.

The applications were endless.

Cedric eventually continued speaking.

"Unfortunately, obtaining large quantities will be difficult."

That pulled me back into reality slightly.

"How difficult?"

"The trees are uncommon even in the south."

Cedric’s expression became more serious.

"And transporting the material this far is expensive, slow, and unreliable."

Leon frowned slightly.

"How much exists there?"

"Not enough to support major demand."

That immediately became a problem.

Even this relatively small amount already felt invaluable to Leon.

Once he started using rubber properly, demand would explode instantly.

Steam engines alone would consume enormous quantities.

And that wasn’t even considering future machinery.

Leon stared down at the latex silently for several moments.

Then suddenly—

"...Can you get a sapling?"

Cedric blinked.

"A sapling?"

"A young tree."

"I know what a sapling is."

Cedric looked genuinely surprised now.

"You want to grow them here?"

My mind already moved ahead rapidly.

Hot climate.

Controlled humidity.

Protected environment.

Glass.

Steam heating.

The thoughts connected almost instantly.

A greenhouse.

Not a simple farming structure.

A controlled growing environment.

Glass panels.

Steam-heated piping beneath the soil.

Temperature regulation.

Humidity retention.

Artificial climate control.

Leon slowly realized his industrial systems already gave him tools this world normally wouldn’t possess.

Most people in this world depended entirely on local climate.

Leon didn’t necessarily have to.

Cedric watched him carefully.

"...You’re doing the stare again."

I barely responded.

"If I can regulate temperature..."

Finn immediately noticed the look in my eyes.

"Oh no."

I looked upward slightly while thinking aloud now.

"Steam pipes could distribute heat evenly through enclosed structures."

Finn pointed aggressively.

"That is the exact tone you use before something dangerous happens."

Cedric looked between the two with growing concern.

"You plan to recreate a southern climate?"

Leon ignored him completely.

Glass panels would trap heat.

Steam systems could maintain internal temperature during colder seasons.

Water channels could regulate humidity.

If successful—

We wouldn’t need southern imports forever.

We could industrialize rubber production directly within the Aldric territory.

I slowly looked back down toward the latex in his hands.

Then toward the steam car behind him.

Then beyond that—

Toward the future again.

Rubber changed everything.

Steam engines.

Factories.

Transportation.

Industrial machinery.

And if he could mass-produce it—

The pace of development would accelerate even further.

Finn rubbed his face tiredly.

"...I recognize that look."

Cedric glanced toward him.

"What look?"

Finn pointed toward me.

"The civilization-altering one."

Leon ignored both of them while staring at the latex.

A greenhouse.

No—

Multiple greenhouses eventually.

Controlled agriculture.

Exotic crops.

Medicinal plants.

Industrial materials.

The moment steam could manipulate climate itself—

An entirely new branch of industry opened.

Cedric eventually cleared his throat slightly.

"I can attempt to acquire saplings."

Leon immediately nodded.

"Do it."

"You haven’t even asked the price yet."

"I don’t care."

Cedric sighed softly.

"That answer terrifies me more than I expected."

Leon finally looked back toward the merchant properly.

"How long?"

"A few months at minimum."

Cedric adjusted one of his gloves calmly.

"Transporting living plants across that distance will be difficult."

"I’ll handle the rest."

Cedric studied Leon silently for several moments.

Then slowly—

"...I genuinely cannot tell whether supporting your inventions is the greatest business opportunity of my life or a catastrophic mistake."

Finn answered immediately.

"Probably both."

And judging by the steam car sitting behind them—

Leon suspected Finn was correct.

——-

Three days later me and Finn finally departed toward Blackwater Hollow.

The trip itself immediately felt strange.

Not because anything happened.

Because almost nothing did.

The roads leading north became cleaner and better maintained the farther they traveled into Nightbane-controlled lands. Forest paths that would normally be rough and uneven elsewhere in the kingdom were surprisingly smooth while stone watchtowers overlooked the roads from elevated hills.

Even the patrols looked different.

Every Nightbane soldier carried themselves with unnerving discipline while dark armor bearing the duchy crest reflected faintly beneath the sunlight. Several soldiers visibly radiated enough mana pressure that I immediately knew they were stronger than most border knights he had seen during the war.

The steam car remained behind for now. Leon still didn’t trust the machine enough for long-distance travel through unfamiliar territory, especially when parts of the engine still occasionally sounded like they were moments away from catastrophic failure.

So instead the two traveled on horseback while carrying rifles, ammunition, and several explosive shells carefully packed into reinforced containers attached to their saddlebags.

Finn kept glancing nervously toward the explosives every couple minutes.

"One bad fall and we both disappear."

"That’s not how explosives work."

"That sounds exactly like something somebody says before exploding."

I ignored him while adjusting the rifle secured along his back.

The weapon itself had already improved considerably since the border war. The firing mechanism had become smoother, the barrel stronger, and Leon had even begun experimenting with grooves carved into newer barrels to improve bullet stability.

The fact he casually traveled with weapons capable of killing trained mages still occasionally felt absurd.

Especially in this world.

By the second evening the forests finally began thinning enough for Leon to see something massive looming in the distance.

The Nightbane capital.

Even from several hours away the city dominated the horizon.

Enormous black walls surrounded the capital while towering structures rose behind them like dark spears cutting into the sky. Mana lights faintly glowed across sections of the outer defenses while colossal watchtowers overlooked the surrounding lands.

Finn stared silently for several moments.

"...That’s a city?"

"It’s the Nightbane capital."

"That looks like the final boss of kingdoms."

Leon honestly understood the reaction.

Compared to most cities inside Valenor, the Nightbane capital looked oppressive simply by existing. The duchy itself rivaled the royal family in influence and military power, and Duke Rosthwall Nightbane was considered one of the strongest individuals in the entire kingdom.

The Nightbanes were not simply another noble family.

They were practically a second throne.

And Blackwater Hollow—

His territory—

Sat completely enclosed inside their lands only a couple hours away from the capital itself.

That fact alone made the entire situation feel insane politically.

No minor noble casually received land surrounded entirely by Nightbane territory.

Especially not land this close to the duchy capital.

I slowly looked toward the distant black city again.

"She definitely planned this."

Finn rubbed his face tiredly.

"I miss when your problems involved normal women."

The next morning the two finally crossed into Blackwater Hollow itself.

At first glance the territory looked disappointingly ordinary to my eyes.

Dense forests surrounded most of the roads while rough hills stretched across the landscape. A weathered sign near the roadside marked the territory boundary while faint smoke rose from one of the villages deeper inside.

Finn looked around suspiciously.

"This is it?"

"Apparently."

"I expected more cultists."

I ignored him while studying the terrain carefully.

Now that they had actually entered the territory, the positioning became even more obvious.

Every road leading outward eventually passed back into Nightbane-controlled lands.

Every trade route.

Every patrol path.

Everything.

Blackwater Hollow practically sat trapped inside the duchy.

If the Nightbanes ever wanted to isolate the territory—

They easily could.

The road eventually led them toward the larger of the two villages.

Compared to settlements within Aldric territory, the place looked cleaner and wealthier despite its small size. Stone wells stood near the center while several larger buildings suggested regular trade passed through from nearby Nightbane settlements and the capital itself.

Several villagers glanced toward Leon and Finn curiously as they entered, though nobody paid them particularly unusual attention beyond the normal suspicion strangers received.

That alone honestly relieved me slightly.

At least Lillith had not somehow informed an entire territory about him this time.

One older villager eventually approached them cautiously.

"You two travelers?"

"Something like that," I answered.

The man’s eyes briefly shifted toward the rifles strapped across their backs before wisely deciding not to ask questions about them.

"Not many people come through here armed like that."

Finn casually rested a hand near one of the explosive satchels.

"We enjoy surviving."

The villager looked even more uncomfortable after hearing that.

I quickly changed the subject before Finn accidentally terrified the locals further.

"How long does it take to reach the capital from here?"

"A couple hours by carriage if the roads are clear."

I just nodded slightly.

Close.

Very close.

Too close honestly.

The more I looked around Blackwater Hollow, the more obvious it became why Lillith selected it. The territory itself wasn’t particularly wealthy or strategically important traditionally.

It was simply near the Nightbane capital.

Close enough that she could probably reach it within a few hours whenever she wanted.

That realization somehow felt more disturbing than if the territory had been important politically.

By the afternoon me and Finn had already learned more about the region through conversations around the village.

Most of Blackwater Hollow consisted of forests and rocky hills with limited farmland. Hunting and logging formed most of the local economy while occasional merchants passed through from neighboring Nightbane lands.

Then during one conversation near the village well—

Leon suddenly heard something interesting.

"...Nobody goes near the old mine anymore."

His attention shifted immediately.

"Mine?"

An older man nodded.

"Northwestern hills."

The villager scratched his beard slightly before continuing.

"Used to produce iron decades ago before the tunnels got overrun."

"Overrun?"

"Giant rats."

Finn immediately frowned.

"...Giant rats?"

The villager nodded seriously.

"Big ones."

"How big?"

The man paused slightly.

"...Big enough."

Finn looked deeply offended by that answer.

Apparently the infestation grew so severe nearly thirty years ago that the mine had eventually been abandoned entirely. Workers disappeared constantly while entire lower tunnel systems supposedly became nests for massive rat colonies.

After enough miners died, operations stopped completely.

Nobody entered the deeper sections anymore.

Most villagers avoided the area entirely now.

But I barely listened to half the explanation anymore.

My mind already raced ahead rapidly.

Thirty years.

An abandoned underground environment.

Dark.

Moist.

Filled with animal waste.

His eyes slowly widened.

Nitrate-rich soil.

Absolute mountains of it.

If giant rat colonies truly inhabited those tunnels for decades, then enormous amounts of waste and decomposition likely saturated the lower mine levels.

Combined with moisture, minerals, and time—

The place might contain massive nitrate concentrations naturally.

Which meant—

I suddenly stood up so quickly several nearby villagers jumped slightly.

Finn blinked.

"...Why do you look excited?"

Leon immediately turned toward him.

"The mine."

"The rat mine?"

"Yes."

Finn stared blankly.

"...You heard the part about giant rats right?"

I could barely heard him anymore.

No waiting months for nitrate beds.

No slowly rationing gunpowder production anymore.

If the mine contained enough nitrate-rich earth—

Everything changed.

Rifles.

Explosives.

Mass production.

The single greatest bottleneck limiting gunpowder manufacturing might disappear overnight.

Finn slowly noticed the look in my eyes.

"...Oh no."

Leon immediately grabbed his shoulder.

"We’re going to the mine tomorrow."

Finn looked horrified.

"The RAT mine?"

Leon was already thinking ahead.

Extraction crews.

Transport wagons.

Refining stations.

If the deposits were large enough, Blackwater Hollow instantly became strategically invaluable.

And because the territory sat entirely inside Nightbane lands—

Any future weapons industry built here would effectively exist under the protection of one of the most powerful families in the kingdom.

The war.

The factories.

The weapons.

Everything accelerated from here.

Finn meanwhile looked like he regretted every decision that brought him to this exact moment.

"...Every time you get excited, my life somehow gets worse."