After Koro-sensei vanished at Mach 20 speed, the basement lab fell into heavy silence.
Both Akira and Erika stood there, staring at the titanium handcuffs slowly taking shape inside the 3D printer.
The soft mechanical hum of the machine suddenly felt unbearably loud.
Akira's ears turned faintly red.
Erika's cheeks were already burning.
Then Selena's cheerful voice suddenly dropped into their minds like a bomb.
"So you're already preparing, huh, brother? Even using titanium at that level~"
Erika's face somehow became even redder.
She opened her mouth—
but no sound came out.
Akira awkwardly rubbed the back of his head and tried to explain.
"It's because… even with my magic restricted, I'm still strong enough to bend normal metal. So I made a titanium alloy version so it would work properly."
Selena's teasing laughter echoed through both their minds.
"Not a bad idea. Erika-chan already promised too, right? Erika-chan~?"
Erika instantly short-circuited.
"I-I… I… I—"
Then she suddenly turned around.
"I-I'm going back to my room! I need to finish my homework!"
She immediately tried escaping upstairs—
but Akira hesitantly reached out and gently caught the edge of her sleeve.
"W-wait…"
Erika froze slightly.
Akira looked away awkwardly.
"Why don't you stay here and do your homework instead? There's enough space here too…"
Erika's heartbeat sped up slightly.
"…What do you mean?"
Akira scratched his cheek, suddenly looking unusually nervous.
"I mean… no, it's just…"
He hesitated for a second before quietly admitting,
"…I thought maybe we could do homework together."
Erika stared at him.
"You said you already finished yours."
Akira went silent briefly.
Then he answered honestly in a softer voice.
"…Fine. I'd just feel happier if you stayed here with me while I worked on the research."
Erika's face turned an even deeper shade of red.
The problem was—
when he spoke honestly like that, she found it almost impossible to refuse him.
"…Fine. Let me get my books first."
She quickly went upstairs.
When she returned a few minutes later, Akira had already prepared a comfortable chair right beside his workstation.
He looked at her with an openly happy and expectant expression.
Erika quietly sat beside him and started working on her homework while Akira focused on analyzing the anti-sensei material data from the scanner.
After a while, Akira glanced toward her notebook.
"Do you… need any help?"
Erika looked up, slightly surprised.
"Huh? No, I'm fine."
Akira tilted his head.
"But you're bad at math, right?"
Erika puffed her cheeks slightly.
"I'm not bad… just not as good at it as other subjects."
Akira smiled gently.
"So I could help you."
Erika hesitated.
"That's high school-level stuff. This is only junior high math. I already understand it."
Akira repeated brightly, almost eagerly,
"I could help."
Erika let out a quiet sigh.
When he looked this genuinely excited, refusing him felt impossible.
"…Fine. Help me then."
Akira immediately brightened and started explaining the problem enthusiastically.
But ten minutes later—
Erika was completely lost.
She had originally asked about a simple junior high math problem.
Akira had somehow taken a simple junior high question into territory that wasn't even taught in high school, making the original problem even more confusing.
She wanted to stop him many times, but seeing how focused and happy he looked while explaining… she couldn't bring herself to interrupt.
So she just nodded along quietly, hoping the scanner would finish soon.
At some point, he unconsciously moved his chair a little closer while explaining.
By the time the scan finally completed.
Akira had somehow ended up teaching her quantum mechanics.
After somehow finishing both their homework and the remaining lab work, Akira and Erika had a quiet dinner together.
Now—
they were sitting in Akira's room.
The titanium handcuffs rested silently on the bedside table, still faintly warm from the 3D printer.
Both of them were blushing intensely.
They sat on the edge of the bed with a very obvious gap between them, neither able to properly look the other in the eye.
The silence stretched painfully long.
Finally—
both of them spoke at the exact same time.
"So…"
They immediately stopped talking again.
More silence.
Erika glanced sideways at Akira and noticed something unusual.
He was quiet.
Not just embarrassed—
actually quiet.
His usual confidence seemed strangely shaken.
She softly asked,
"…Are you okay?"
Akira stared down at his hands for a few moments before answering.
"…I think so."
Erika moved slightly closer.
"Really?"
Akira hesitated.
Then, surprisingly honestly, he admitted,
"…Maybe I'm a little afraid."
Erika smiled gently.
"That's a lie. I've never seen you afraid of anything."
Akira shook his head.
"That's not true. I'm afraid of lots of things."
"Like what?"
"Bugs."
He paused seriously.
"More specifically… creepy crawlies."
Erika's smile widened slightly.
"You're not afraid of them. You're disgusted by them. That's different."
Akira scratched his cheek awkwardly.
"Well… maybe when our lives were in danger?"
Erika looked at him quietly.
"I've never seen you afraid. Not even back then when we were children and surrounded by werewolves."
Her expression softened.
"Because you knew you could save us. At least me."
Akira went silent for a while.
Then he quietly said,
"Well… I don't really know."
He looked away slightly.
"But I think it's probably the same feeling I had when I confessed to you."
Erika's cheeks turned faintly pink again.
"I see…"
Akira continued quietly.
"Or the feeling I got when I accidentally walked in on you bathing…"
Erika paused.
But Akira kept talking without noticing.
"Or the time before that in the Demon Slayer world… or the time before that when we…"
He suddenly frowned.
"Wait…"
He looked genuinely confused.
"Why do I keep accidentally walking in on you bathing so often?"
Erika's expression went completely blank.
"That's because you're an idiot who can't knock for some reason."
Akira accepted that immediately without even arguing.
Then he continued honestly.
"…It's kind of like that."
He stared quietly at the floor.
"I don't know if it's fear or something else, but… whenever we get closer… or take another step forward…"
His voice softened slightly.
"I get this feeling."
Erika's heart tightened immediately.
She understood exactly what he meant.
For a few seconds, both of them looked at each other—
then immediately looked away again.
Finally—
Selena completely lost her patience.
Her telepathic voice exploded into both their heads.
"For the love of— You two already do things like this normally! Why are you acting like this is your wedding night?!"
Erika immediately turned the reddest she had been all day.
"Selena! Don't make it even weirder!"
Akira went completely silent.
But Selena continued mercilessly, sounding genuinely exasperated now.
"Just start already. How long are you two planning to sit there?!"
After Selena's teasing words, the room fell into a heavy, charged silence.
Erika's face remained deeply flushed.
Her eyes slowly drifted toward the titanium handcuffs on the bedside table—
then toward Akira.
"…Maybe we should start."
Akira nodded slowly.
For once, even his usual confidence seemed subdued by obvious nervousness.
Erika gently helped him lie back onto the bed.
Her hands trembled slightly as she carefully fastened one cuff around his left wrist—
then the other around his right.
Click.
Click.
Now Akira was fully restrained to the headboard, both arms raised above him.
Erika hovered over him awkwardly for a moment.
The position itself felt dangerously intimate.
She was basically straddling him now, their faces only inches apart, neither of them entirely sure how to continue.
Both of them were breathing slightly faster than normal.
Slowly, Erika leaned down until her body rested against his.
Then—
she lowered her head.
Her fangs gently pierced the side of his neck.
The moment his blood touched her tongue—
something inside her shifted.
Erika's eyes turned a deep, hazy crimson.
Her instincts immediately surged to the surface.
She began drinking far more greedily than usual, completely unlike her normal elegant restraint.
Her arms wrapped tightly around him as if she was afraid he might disappear.
Her body pressed flush against his.
Even after drinking the amount she normally would—
she still didn't stop.
Instead, she shifted slightly and bit the opposite side of his neck too, continuing to drink desperately, almost possessively.
Meanwhile—
Akira's mind was in complete chaos.
He could feel everything.
The weight of her body resting on top of him.
The warmth of her skin through their clothes.
The slight trembling in her body as she drank from him.
New, unfamiliar sensations kept crashing into his thoughts, throwing his brain into complete overdrive.
And with both his hands restrained—
he had absolutely no idea what to do.
Especially when Erika suddenly lifted her head slightly and looked down at him with those glowing crimson eyes.
At that moment—
an overwhelming impulse suddenly hit him.
He wanted to lean up and bite her lips.
Selena's telepathic voice immediately cut into his thoughts, sounding both amused and exasperated.
"That's called a kiss, you know."
Akira instantly snapped back telepathically.
"Now is NOT the time! I don't think she's fully in control right now!"
Selena sighed lightly.
"I don't think she's completely out of control either. She's trying her best here, okay? But yes… she's a little out of it."
Akira swallowed hard.
"And I can't even help her here…"
Selena immediately teased him again.
"Don't you want to kiss her? Would you help her if your hands were free?"
Akira shot back instantly.
"Oi, sis—help me here! Stop joking around!"
Selena only laughed softly.
"Just let her be. She'll calm down eventually. Good luck, okay?"
Then she went silent again.
Meanwhile, Erika continued clinging to him as though she was finally releasing everything she had been suppressing for so long.
Her grip tightened.
Her breathing grew heavier.
She pressed herself even closer against him.
Eventually—
after finally drinking her fill—
her movements gradually slowed.
The crimson glow in her eyes softened turning back to it's usual blue.
Then her body suddenly went limp.
Erika slowly passed out on top of him.
Akira breathed heavily.
He had lost a considerable amount of blood—
but honestly, that wasn't what worried him most.
Erika had completely passed out on top of him.
"Erika…?" he called softly.
No response.
She was breathing peacefully, fast asleep with her face buried against his neck.
Her instincts had finally calmed down, but even unconscious, her body still clung tightly to him.
And meanwhile—
Akira was still completely handcuffed to the bed.
Fully trapped.
For a moment, he considered waking her up.
But when he looked down at her peaceful sleeping face…
he simply couldn't bring himself to do it.
So instead, he quietly stayed still.
Feeling her warmth.
Her steady breathing.
The rhythmic heartbeat pressed against his chest.
And the way her arms unconsciously held onto him.
After a while, he quietly muttered to himself,
"…This is actually kind of nice."
His expression softened slightly.
"It's rare to be this close to her. Maybe this is okay."
It wasn't the first time they had slept beside each other.
But normally, he was always the one who fell asleep first and woke up later.
So for once—
he decided to fully enjoy this rare situation.
…Just a little longer.
—
Ten minutes later.
"…My arms hurt a little, but it's fine. I've endured worse."
—
One hour later.
"…I'm kind of thirsty now. But it's okay. I can survive days without water."
—
Three hours later.
"…Oh no."
His expression slowly stiffened.
"This is bad… I really need to—"
He looked down at Erika again.
She was still sleeping so peacefully.
And suddenly, Akira found himself trapped in the greatest battle of his life.
Wake her up?
Or endure it?
He genuinely didn't know what to do.
Because if he woke her up—
she might get embarrassed and move away.
And this situation was such a rare opportunity…
Finally, in complete desperation, Akira called out telepathically.
"Sister… save me…"
No response.
"Sister?"
Nothing.
Selena had completely abandoned him during his moment of greatest need.
Akira struggled internally for a long time.
In the end—
he made his decision.
He would endure it until Erika woke up naturally.
—
Early the next morning—
Erika slowly woke up.
She had slept unusually well.
Honestly, more comfortably than she had in a long time.
Still half-asleep, she stretched slightly before opening her eyes.
The very first thing she saw—
was Akira's face.
His eyes looked utterly dead.
Not tired.
Not sleepy.
Dead.
Like a man who had been tortured for ten straight years.
Erika nearly jumped out of her skin.
"Akira?!"
Akira slowly turned his head toward her with exhausted, lifeless eyes.
Then, in a hoarse voice, he quietly said,
"…Can you please unlock these handcuffs? I need to pee."