The morning sky was a brilliant, piercing blue. I woke up in my room, surrounded by stacks of my favorite light novels—the Monogatari series. Exhaustion still clung to my bones as I dragged myself to the bathroom. Brushing my teeth, I caught my reflection in the mirror.
"Not bad looking, if I do say so myself," I muttered under my breath.
"Nii-chan! Hurry up and come down! Breakfast is ready!"
That was the voice of my cute little sister. But before we go any further, allow me to introduce myself: I am Shinomiya Itsuka, a man who lives and breathes mystery stories. I headed down the stairs to find my adorable sister waiting. She's fourteen, a middle schooler at an all-girls academy, so she rarely interacts with guys—aside from me.
"Nii-chan, it's 8:00 AM. You're going to be late," Shiro said. Her gaze was flat, her expression weary, as if she were looking at something particularly troublesome.
"Calm yourself, my beloved sister," I replied with a faint smirk. In one dramatic movement, I leaned in and gently lifted her chin.
Shiro stared at me with zero expression for two full seconds, as if evaluating a piece of junk, before swiftly swatting my hand away.
"Please stop. You're being disgusting this early in the morning," she said, her voice a cold, level drone. However, my keen amateur detective's eyes caught the slight flush of red creeping onto the tips of her ears.
I chuckled and pulled out a chair. On the table sat a simple breakfast: two slices of strawberry jam toast and a perfectly fried sunny-side-up egg.
I took a bite, savoring the flavor. "Shiro's cooking really is the best. If it stays like this, Nii-chan might never be able to live without you."
Shiro, sipping her milk, turned her face toward the window. "Don't talk nonsense while you're chewing. Besides, I only made breakfast because I didn't want you dying of hunger in your room and bothering me with funeral arrangements."
Typical Shiro. Her words were always ice-cold, yet the yolk on my plate was runny—exactly the way I like it.
In this two-story house that feels a bit too spacious, it's just the two of us. Our parents have been gone for a long time. There was no grand conspiracy or convoluted mystery behind it like the detective novels I read; it was just a mundane traffic accident years ago. At least, that's what I tell myself. The insurance money and their savings were enough to secure our lives and education until we graduate university.
That's why, to me, the definition of 'family' is simple: just me and Shiro. And as the only man in this house, protecting her is my absolute duty.
"Ah, crap! It's ten past eight!" I shouted after glancing at the wall clock. I bolted down the rest of my toast and gulped some water. "I have to run. Aren't you heading out, Shiro?"
"My school is closed today for the foundation's anniversary," she answered flatly, starting to stack my dirty plates. "Just go already. Staring at Nii-chan's face in the morning is making me lose my appetite."
"How cruel!" I wailed dramatically, swinging my school bag over my shoulder and half-running toward the genkan.
As I hurriedly shoved my shoes on, I glanced back. Shiro was standing at the edge of the kitchen hallway. Her face was still expressionless, a dishcloth in her hand, yet she remained there—waiting for me to actually leave the house.
I smiled at the sight. "I'm heading out, Shiro!"
"...Take care, Nii-chan."
Her reply was incredibly soft. It was barely a whisper, like a passing breeze, but my ears caught it loud and clear.
I opened the door and stepped outside. The morning sun stung gently, and clouds drifted lazily across the vast blue sky. It was a peaceful day. A normal morning routine, the usual bickering, and a cute kuudere sister.
However, as I walked down the sidewalk toward school, my "mystery enthusiast" instincts began to prickle. The morning air felt... different. It was as if this boring peace was merely the silence before a true storm.
And I was right. My normal, peaceful life with my sister was about to be dragged into a twisted riddle—one that had never existed in any mystery novel before.
-END OF PROLOGUE-