Prologue

November mornings should have made crawling out of bed an absolute misery, but on this particular day—

“Uuu… uuu~… hm? Eh? ── WHOAAAA──────!?”

I didn’t wake up refreshed. I woke up in complete shock.

“Akira, why are you sleeping in my bed!?”

I certainly didn’t remember agreeing to this arrangement. Yet there was my step-sister, curled up like a small animal inside my futon—naturally, I’d be startled out of my mind.

“Uuun… Anikiii… I’m still sleepy~…” she mumbled drowsily.

The mastermind behind my morning heart attack rubbed her sleepy eyes and stared intently at my bewildered face for a moment. Then, as casually as if nothing unusual had happened, she pulled the covers back over herself and began drifting off to sleep again.

“── Hey, wake up!” I protested.

“…What~?”

“Don’t ‘what’ me! Why are you sleeping in my bed? How long have you even been here?”

Perhaps because the room was cold, Akira had wrapped herself in the futon like a cocoon, looking undeniably cute in the process. But this wasn’t a situation that could be brushed off with mere cuteness alone.

This morning shock was, in its own way, more jarring than a flying body press first thing after waking up—my heart felt ready to burst from my chest.

“Um, I came to wake up Aniki this morning,” she explained matter-of-factly.

“…Okay, and then?”

“Aniki was sleeping so peacefully.”

“…And so?”

“I got into Aniki’s bed.”

“…Furthermore?”

“I went to sleep too. ── Yep, that’s it.”

“Hey, wait just a minute there! That doesn’t explain anything at all, y’know?”

“Aniki’s really energetic this morning~” she observed cheerfully.

“Whose fault do you think that is!” I shot back. “Akira, you’re usually── whoa!”

Without warning, Akira’s arm shot out toward my neck, pulling me forcefully in her direction. When I lost my balance and my head bumped against the pillow, her face was suddenly right in front of mine.

She stared at me silently with drowsy, half-lidded eyes that seemed to peer straight through me.

“Wh-what…?” I stammered.

“Come on, let’s sleep just a little more, ’kay?” she suggested sweetly.

“Wait, hold on—sleep? Right now? With you!?”

“Yep. Aniki’s my body pillow~”

“Hey, your face is way too close! Stop squirming around! It’s morning, so we need to get up! And stop being half-asleep!”

“Body pillows shouldn’t move around so much~” she replied with drowsy logic.

Akira’s strength was surprisingly formidable, and the more I resisted, the more force she applied in response. With that incredible suction power of hers, I had no choice but to stop struggling—though that’s not to say I was giving up. I was simply waiting for the right moment when Akira let her guard down to make my escape. It definitely wasn’t because she was warm, soft, sweet-smelling, and possessed such a calming, pleasant fragrance that made my resistance waver. …Really.

“…Akira-san, could I ask you something?” I said, switching to a more formal tone.

“Yes, go ahead,” she replied agreeably.

“Why are you being such a clingy little sister this morning? You’ve never snuck into my bed on your own initiative before, right?”

“Eh? Aniki, you don’t know what day it is today?”

What day? Some kind of anniversary perhaps? Maybe it was a special occasion that had completely slipped my mind?

“I don’t know. Tell me.”

“Today is Culture Day.”

[T/N: Culture Day is a public holiday in Japan held annually on November 3 to promote culture, the arts, and academic endeavour.]

I see.

………

…………..And?

“How exactly does that relate to you sneaking into my bed?”

“Little sisters sneaking into their big brother’s bed is totally a proper Japanese tradition, y’know?” she declared with complete confidence.

“Ah, I see! ── Hey, wait a minute! What do you think Japanese culture is!?”

“Yeah, yeah, it’s fine, it’s fine~, let’s just sleep together~”

I clutched my head in exasperation, first thing in the morning.

This step-sister of mine was far too free-spirited, far too peaceful, and far too cute for a day supposedly dedicated to celebrating freedom, peace, and cultural advancement.

Should we really be promoting this particular interpretation of culture? Absolutely not.

“This really isn’t good for big brother’s mental health, y’know…” I muttered.

“Don’t sweat the small stuff~” she dismissed cheerfully.

“No, no, no, no—this is pretty major stuff, you know…”

Akira apparently had no intention of pursuing this discussion any further. She burrowed even deeper into the futon and nuzzled her face against my chest, settling in for another round of sleep.

What an incredibly spoiled sleepyhead. I clutched my head even harder in despair.

── But just then, I heard someone coming up the stairs.

Those familiar footsteps gradually approached my room and finally knocked on the door with characteristic enthusiasm.

“Ryouta, you awake~?”

People who can’t read the atmosphere, won’t read the atmosphere, and have absolutely no intention of reading the atmosphere do exist in this universe. For example—

“I’m coming in even if you’re sleeping~”

── like Majima Taichi, our old man…

Oh crap! If he finds us like this!

The next moment, my desperate course of action was—

“I wanted to talk about something… hey, if you’re awake you could at least answer, y’know?” he called out.

“Ah, yeah, sorry about that, old man…” I replied as naturally as possible.

Right now I was sitting upright with my hands positioned behind me, knees bent strategically under the covers. From the old man’s perspective, the futon probably just looked normally tented up—hopefully appearing completely natural.

But actually, inside the futon—I had pushed Akira’s head down around my stomach area, with her entire body squeezed carefully between my legs.

Basically, if those covers got pulled back, we’d be completely and utterly screwed—

“I was just thinking about getting up…” I added casually.

“Well, if you’re awake, that’s perfect timing!” he announced cheerfully.

── but somehow I managed to fool the old man’s observant eyes.

“More importantly, get ready to celebrate! This is big news!”

There might indeed be bigger news than discovering your step-sister had snuck into your bed, but right now I didn’t have the confidence to be genuinely surprised by anything else.

I should at least act appropriately surprised out of filial duty.

“So, what’s── hyah!?” I started to ask.

“Hm? Something wrong?” he inquired.

“N-no, nothing at all──”

── Why is she stroking my stomach!?

I couldn’t help but glare down at the suspicious lump in the futon with barely contained panic.

Somehow I managed to laugh it off convincingly, but the tickling sensation was so intense that I’d accidentally let out that strange sound. …She was definitely getting a serious lecture about this later.

“S-so, what’s this big news about?” I asked, trying to regain my composure.

“You know how your school has that four-day weekend around Labor Thanksgiving Day, right? Well, both Miyuki-san and I managed to get time off too!”

“O-oh yeah…? And?” I prompted, though part of my attention remained focused on the mischievous presence hidden beneath my covers.

“So we’re going!” he announced triumphantly.

“Going? Where exactly?”

“Family trip! A two-night, three-day hot springs trip!”

“Hot springs… family trip…?” I repeated, the implications slowly sinking in.

“Man, I’m so pumped~! Anyway, everyone gather in the living room right now! And wake up Akira while you’re at it!”

After delivering that bombshell announcement, the old man bounded back downstairs like an excited child, shouting “Yahoo!”

Immediately after that, something tumbled loudly down the stairs.

“Kyaa! Taichi-san!? Are you okay!?”

My step-mother Miyuki-san’s concerned scream rang out from below, but I found myself clutching my head even harder than before.

Because—

“Funya~ …Aniki’s abs are so hard~. …Ehehe~♪”

── this was the current situation…

My step-sister, completely melted with a blissful expression while half-asleep against my abs, utterly content in her impromptu resting spot.

Combined with a pretty hopeless old man, a slightly airheaded step-mother, and our very first family trip to a hot springs resort…

When all these chaotic factors mixed together, I couldn’t shake the growing feeling that some major incident was absolutely bound to happen.