The Yandere villainess loves the useless engineer

The next day passed in complete silence.

I remained locked inside my room while sunlight slowly shifted across the floorboards beneath the window.

I ignored everyone.

Mother tried speaking through the door.

Father knocked a couple times before eventually giving up.

Even Alex attempted cheering me up once, though after several minutes of silence he awkwardly walked away muttering something about "giving me space."

And Lilith...

Lilith came the most.

Every couple hours, soft knocks would echo from the other side of the door.

"Leo?"

Silence.

"...Are you awake?"

Silence.

"You should eat something."

Still silence.

Eventually, even her voice would fade away down the hallway.

Honestly, I felt pathetic.

For years, I had obsessed over magic.

This world revolved around mana.

Strength.

Power.

And now I had none of it.

I sat quietly beside the window staring blankly outside.

The forests surrounding the manor swayed gently beneath the afternoon breeze.

Then suddenly—

A bird soared between the trees.

My eyes followed it instinctively as it glided effortlessly through the air before disappearing beyond the horizon.

And for the first time in nearly an entire day—

My thoughts drifted somewhere else.

Back.

Back to my old world.

Back before reincarnation.

Back when I was still an aerospace engineer.

I could still remember it clearly.

The endless nights spent hunched over blueprints.

The stacks of textbooks scattered across my apartment.

Aerodynamics.

Combustion systems.

Structural engineering.

Propulsion.

I remembered every sleepless night spent studying aircraft designs over and over again.

Every equation.

Every diagram.

Every prototype.

Even after thirteen years in this world, none of it had faded.

Not even slightly.

And suddenly—

Something clicked inside my head.

Magic wasn’t the only path to power.

My eyes slowly widened.

"...Wait."

I abruptly stood up from the bed.

This world had magic.

But technologically?

It was primitive.

Their weapons were basic.

Their transportation was outdated.

Most people still relied almost entirely on mana for advancement.

Which meant—

The knowledge inside my head alone could completely change this world.

A slow grin spread across my face.

Planes.

Engines.

Firearms.

Industrial machinery.

Even basic engineering concepts here would look revolutionary.

Magic or not—

I could still dominate this world.

The hopelessness crushing my chest since yesterday slowly began fading away.

In its place—

Excitement returned.

No.

Determination.

If I couldn’t become powerful through mana—

Then I’d simply build power with my own hands.

I immediately rushed toward the door.

But the moment I swung it open—

"OW!"

A figure tumbled backward onto the floor.

I blinked.

Lilith rubbed the back of her head while glaring up at me from the floor.

"You opened that way too fast..."

"...Were you sitting outside my door?"

Lilith avoided eye contact.

"...Maybe."

I stared at her blankly.

"How long?"

"...Since this morning."

"...Lilith."

"What?" she mumbled defensively. "I was worried."

A strange warmth flickered briefly in my chest.

I let out a tired sigh before offering her my hand.

Lilith immediately grabbed it, allowing me to pull her back to her feet.

For a moment, she studied my face carefully.

"...You look better."

"I feel better."

Lilith visibly relaxed slightly at those words.

Then almost immediately—

"So," she began casually, "about the marriage thing—"

"No."

"You didn’t even let me finish."

"I already know where this is going."

Lilith puffed her cheeks slightly.

"You should still marry me."

I rubbed my forehead tiredly.

"Lilith, we’re thirteen."

"So?"

"So normal people don’t decide marriage this early."

"You’re avoiding the question."

"I’m surviving emotionally."

Lilith crossed her arms before narrowing her eyes at me.

"...Then when?"

I paused for a moment before eventually answering.

"When we’re older."

Lilith blinked.

"You’ll think about it when we’re older?"

"...Yeah."

For several seconds, Lilith stared at me silently.

Then unexpectedly—

A faint smile slowly appeared on her face.

"...Okay."

That was suspiciously easy.

I decided not to question it.

Instead, I grabbed my coat and started walking down the hallway.

Lilith immediately followed behind me.

"Where are you going?"

"To change the world."

"...What?"

"I need a workshop."

Lilith looked completely confused but continued following anyway.

————

Several hours later, the two of us sat inside a crowded tavern near the edge of town.

Originally, I planned on searching for abandoned buildings or cheap properties where I could begin working privately.

Unfortunately—

Everything was either too expensive or too public.

"This is harder than I thought," I muttered.

Lilith calmly sipped her drink beside me.

"You’re being picky."

"I need privacy."

"You sound suspicious."

Before I could respond, loud laughter echoed from a nearby table.

A group of older men sat drinking together while loudly talking amongst themselves.

"One of these days I’m just gonna sell that damned shack already," one grumbled.

Another man laughed.

"The one in the woods?"

"Aye. Nobody wants it though. Too far from town."

My ears perked up instantly.

I slowly turned toward Lilith.

She blinked.

"...Why are you smiling like that?"

————

About twenty minutes later, negotiations were complete.

For a surprisingly small amount of money, I had officially purchased an old abandoned shack deep within the nearby woods.

Apparently, most people avoided it because of its isolated location.

Which made it perfect.

After nearly an hour of walking through the forest alongside Lilith, we finally arrived.

The shack itself looked old and worn down, partially hidden amongst thick trees and overgrown vegetation.

Honestly—

It looked terrible.

But the moment I saw it, ideas immediately flooded my mind.

A private workshop.

A testing area.

A laboratory.

My imagination spiraled wildly with possibilities.

Steam engines.

Primitive firearms.

Experimental aircraft concepts.

The future practically unfolded before my eyes.

Meanwhile, beside me—

Lilith looked incredibly unamused.

She stared blankly at the broken shack before slowly turning toward me.

"...This is your grand plan?"

I looked back at the building with shining eyes.

"...It’s beautiful."

Lilith stared at me like I had completely lost my mind.

By the time Lilith and I returned to the manor, the sky had already begun turning orange beneath the setting sun.

The servants near the entrance immediately bowed as we approached, though several of them looked visibly confused seeing dirt covering parts of our clothes after spending hours wandering through the forest.

Lilith, meanwhile, still looked mildly offended by the existence of the shack.

"I still don’t understand why you’re so excited over a broken building," she muttered as we walked through the halls.

"You lack vision."

"It has holes in the roof."

"It has potential."

"It has mold."

"That just adds character."

Lilith stared at me blankly before sighing dramatically.

"You really are strange sometimes, Leo."

I smirked slightly.

"And yet you still follow me everywhere."

"...That’s different."

We eventually reached one of the quieter balconies overlooking the manor gardens. The evening breeze drifted gently through the air while the sounds of servants preparing dinner echoed faintly from deeper inside the estate.

For once, neither of us spoke immediately.

Then Lilith quietly stepped beside me.

"...I have to leave tomorrow morning."

I blinked slightly.

"So soon?"

Lilith gave a small nod.

"Father already delayed our return longer than planned because of your ceremony."

Right.

Honestly, after everything that happened recently, I had almost forgotten she technically lived several territories away.

Still...

The thought of her leaving made the manor suddenly feel quieter already.

Lilith leaned lightly against the balcony railing.

"And..." she hesitated briefly, "...I probably won’t be able to visit as much anymore."

That caught my attention immediately.

"What do you mean?"

Lilith looked away toward the fading sunset.

"Father enrolled me into the Royal Academy in the capital."

My expression stiffened slightly.

The Royal Academy.

That was the most prestigious academy in the entire Kingdom of Valenor.

Only nobles and exceptionally talented individuals were accepted there.

Which obviously meant Lilith was practically guaranteed entry after awakening publicly as an A-rank.

"I’ll mostly stay in the capital from now on," she continued quietly. "I’ll only return to the Nightbane Territory during the winter and summer months."

For some reason, hearing that left a strange feeling in my chest.

I had gotten used to her constantly appearing around the manor.

The idea of months passing without seeing her felt... odd.

Lilith glanced toward me carefully.

"...Does that bother you?"

I stayed silent for a moment before eventually answering honestly.

"...A little."

The instant those words left my mouth, her eyes widened slightly.

Then slowly—

A soft smile appeared on her face.

"...Good."

I narrowed my eyes slightly.

"That response sounded suspicious."

Lilith ignored me completely.

"You should come visit the capital someday."

"Maybe."

"You better."

I chuckled lightly.

For a while, the two of us simply stood there watching the sunset quietly together.

Then Lilith suddenly spoke again.

"When I come back during winter..." she paused briefly, "...you’ll show me your workshop, right?"

I grinned slightly.

"Of course."

Lilith looked at me silently for several seconds.

"...I’m looking forward to it."

————

The next morning arrived far too quickly.

A large black carriage bearing the Nightbane crest waited outside the manor while several knights prepared for departure nearby.

Mother and Father stood near the entrance offering farewells while Alex awkwardly thanked Lilith for helping me after the ceremony.

Meanwhile, I stood slightly off to the side watching as servants loaded the final luggage into the carriage.

Eventually, Lilith walked over toward me.

For once, she seemed quieter than usual.

"You better not forget me while I’m gone," she said softly.

I snorted lightly.

"You say that every time."

"Because it’s important."

I shook my head slightly before answering.

"I won’t forget you."

Lilith stared into my eyes carefully, almost like she was trying to confirm whether I truly meant those words.

Then slowly—

She stepped forward and hugged me tightly.

This time, I hugged her back without hesitation.

After several quiet moments, Lilith finally pulled away.

"...I’ll see you in winter then."

"Yeah."

She lingered for another second before eventually turning and walking toward the carriage.

Right before stepping inside, she looked back at me one final time.

Then the carriage doors closed.

A few moments later, the Nightbane knights began moving.

I watched silently as the carriage slowly disappeared down the road beyond the manor gates.

And just like that—

Lilith was gone again.

————

A little while later, I returned to my room and immediately began preparing supplies for fixing up the shack.

Tools.

Paper.

Candles.

Anything remotely useful.

If I was serious about building a workshop, I needed to start immediately.

As I moved around the room gathering supplies, something suddenly caught my attention.

My wardrobe door was slightly open.

I frowned.

"...I swear I closed this earlier."

Maybe one of the servants opened it while cleaning.

Shrugging it off, I walked over and shut the wardrobe door properly before returning to packing.

Far away from the Aldric Territory—

Inside the Nightbane carriage moving along the forest roads—

Lilith sat quietly beside the window.

Folded carefully within her hands rested a shirt and pair of pants belonging to Leon.

She held the fabric gently against her chest while a soft smile spread across her face.

The deep purple glow within her eyes flickered faintly for a brief moment.

"...Leo..."

Her fingers tightened slightly around the clothes.

"You really are too careless."

Lilith buried part of her face into the fabric, inhaling softly before whispering quietly to herself.

"No matter where you go..."

A possessive warmth filled her voice.

"...you’ll be mine."