Tokyo's trains were always busy, the rhythmic clatter of wheels against steel weaving together a melody unique to city life.
After transferring carriages twice, Kasumigaoka Touji and Kasumigaoka Utaha finally found a rare, empty seat near the window.
"You sit," Touji offered politely, motioning toward it with a faint smile.
"No, no, otōto-kun, you should sit," Utaha countered gracefully, tucking a loose strand of hair behind her ear.
Ah, the eternal battle of polite siblings.
Touji glanced sideways at her, then smirked mischievously. "Then how about this—why don't you just sit on my lap? That way, we both win."
"...Stare—"
Those wine-red eyes locked onto his face with a piercing intensity, shimmering ever so slightly.
They stared at each other in silence for a few seconds, the gentle sway of the train accompanying the tension.
Then, Utaha gave a small nod, almost imperceptibly.
Touji immediately slid into the seat, straightening his back like a proper chair.
Utaha elegantly gathered her pleated skirt with her fingertips and slowly lowered herself onto his lap, settling in with the grace of a noblewoman.
The soft warmth of her body, the subtle scent of her shampoo, and the faint trace of her lotion mixed into an intoxicating blend that washed over Touji's senses.
Unable to resist teasing, Touji leaned close to her ear and whispered playfully, "Utaha, just out of curiosity… how much do you weigh? You feel kind of... substantial~."
Utaha's body stiffened slightly. "Ninety-nine pounds," she replied flatly, keeping her expression cool.
"Huh? But weren't you already heavier than that last year?"
"That was last year. I've slimmed down since then," she shot back coolly.
Total lies! You definitely went up a size!
"Do you think I'm heavy, Touji-kun?"
She couldn't reach him easily while perched on his lap, so instead, she stomped lightly on his foot.
"Not at all! In fact, it's the perfect weight! Very soothing! Also… ow, you're stepping on my foot."
"Oh? Gomen, I didn't notice~" she said, not even trying to hide the smug curve of her lips.
"…Tch."
From the corner of his eye, Touji caught an old man nearby with a deeply disapproving look, the classic "grumpy commuter uncle holding a phone" expression.
Realizing the public nature of their little flirting session, both of them reluctantly toned it down.
...
By the time they got home, the clock had ticked past 3:30 PM.
Utaha headed to the yard to bring in the laundry, while Touji trudged upstairs to his room.
It was still early, so no need to start dinner yet.
He planned to knock out some homework and—if he had time—transcribe a new song.
Initially, he'd wanted to submit "Blue Bird" for the school's music program. Yep—the iconic third opening from Naruto Shippuden. A total banger.
Touji had already prepared everything for it.
But then… things between him and Utaha changed.
Something shifted.
Now, he wanted a song that reflected her—her elegance, her mystery, her contradictions. Something personal.
In the world he came from, Kasumigaoka Utaha had a couple of "theme songs"—like "Rap Scandalous" and "LOVEiLLUSION." Catchy, sure… but they didn't capture what he felt for her.
So he'd make a new one.
...
Meanwhile, downstairs, Kasumigaoka Utaha had just finished gathering the laundry and stepped into the living room. Her gaze casually landed on the digital scale resting quietly in the corner near the hallway.
The moment she saw it, a flash of memory played in her mind—Touji's cheeky words from the train ride earlier.
"…Substantial, huh?" she murmured.
Utaha put the folded clothes aside, walked over with graceful steps, and stood before the scale. With a small sigh, she slipped off her indoor slippers, revealing her feet wrapped in elegant black stockings—each toe perfectly outlined, as if painted by an artist.
She stepped onto the cold scale surface with practiced ease.
Beep—beep—beep.
The numbers flickered, blinking rapidly.
Finally—52.0 KG.
"...Gained two more pounds," she whispered, blinking blankly at the numbers.
"No way."
She instinctively placed a hand on her chest, then trailed down her waist and gave her bottom a gentle pat. Everything felt just right. The curves were still balanced, her waist still slender—if anything, it had all gone to the right places.
Her cheeks flushed just a little.
After all, her otōto-kun was a total chest-con, waist-con, butt-con, leg-con, foot-con, face-con… not to mention an unrepentant sister-con.
"Fufufu… I must look even more irresistible to him now~."
Still, she reminded herself, it wouldn't do to slack off. Many women gained weight slowly without realizing it—thinking they were fine until they were too far gone.
Utaha frowned slightly.
"I guess… I should try doing yoga at night too. Good for shaping and keeping my flexibility."
Her mother practiced yoga religiously at home. Maybe she could ask for pointers?
With that thought in mind, Utaha ascended the stairs, carrying the neatly folded clothes and her school bag in one arm. She gently knocked, then opened Touji's door and peeked in.
"Otouto-kun, are you doing your homework?" she asked softly.
"Yeah," Touji replied, not even turning around. His pen moved steadily across the page—it looked like English homework.
"I'm putting your clothes in the wardrobe," she said, stepping inside.
"Okay. Thanks."
Their conversation ended there.
Utaha blinked, let out a small sigh, and quietly walked out, her footsteps light against the wooden floor.
...
Touji finished his homework within thirty minutes and switched on his computer. With a few clicks, he opened his music folder on drive D and created a new text file.
"Time to work," he muttered.
He racked his brain, flipping through the catalogue of anime songs in his memory.
Nothing quite fit.
What he needed was something that captured a forbidden love kind of vibe.
It couldn't be a typical youth romance. No, no… it had to be emotionally charged. Like… something between siblings. Something taboo.
"That's it… I'll just adapt one."
A spark lit up in his mind.
There was a song—"14 to 1"—the ending theme of a certain anime where a girl suddenly found herself with thirteen brothers after her father remarried. As the episodes unfolded, her feelings turned complicated—some of those brothers weren't entirely… brotherly.
"Perfect. Close enough!"
With the idea in place, Touji began typing furiously, recalling the original lyrics as best he could and modifying them to suit his and Utaha's situation.
[my elder sister (my older sister)
I really like you very much
I hope you can choose me
Let me protect your bright smile
And your faint eyes
It has already overflowed
It has long surpassed the boundaries of siblings…]
Touji sat back and grinned.
"Yosh! Got the bones of it down!"
He leaned back in his chair, looking pleased.
The sun outside had begun to dip, casting golden-orange rays into his room. A glance at the bottom right corner of his screen told him it was nearly 5 PM.
"Time to make dinner…"
He stood up, stretched lazily, and headed downstairs.
This song—it was going to be their song.
One that could never be played at a normal school concert…
But that didn't matter.
It was a secret melody meant only for the two of them.