It was already dark outside.
Aika quietly descended the dimly lit stairs of Ryosuke's house and headed toward the entrance.
Coming home always made her feel incredibly lonely.
Ryosuke never saw her off. That was fine. She had received more than enough love from him; to ask for more would be presumptuous.
"..."
Still...
The heat from his touch on her skin and the roughness inside her body still lingered, and every time it throbbed, she felt the ache of loneliness. More. More. It still wasn't enough...
"Aika-san."
Startled by the sudden voice behind her, Aika flinched and froze. Turning around, she saw Ryosuke's younger sister standing there.
"Marin-chan..."
"Brother is such a jerk, isn't he? He should at least see you out."
"Such..."
Meeting her in the dim light was enough to give anyone a heart attack.
Her bangs were neatly trimmed. Her long black hair hung straight and smooth. She was still wearing her school uniform, even on a day off—had she worn it all day?
"Older Brother is just lazy when it comes to getting dressed, I bet. He's surprisingly slovenly, despite how he looks."
I can't tear my eyes away from Marin as she approaches.
She's my adoptive younger sister, Ryosuke's younger sister, always carrying that faint smile on her face.
Every time I see her, I think of a thin, sharp blade and shiver. Imagining her tearing me apart, my legs tremble.
"Aika-san, you've been wearing that hairstyle lately, right?"
"..."
Aika stammers, unable to answer, and falls silent.
Marin's flawless beauty is overwhelming. The closer I look, the more I feel it.
Her large, almond-shaped eyes are captivating, with their dark irises and alluring gaze. A straight nose bridges to thin, pale pink lips, and her jawline is delicate, framed by luminous skin.
She's so perfectly formed that she lacks any sense of vulnerability, somehow doll-like.
Despite having no blood ties to Ryosuke, there's something about her that reminds me of him. Is it her expression? Or perhaps those piercing eyes?
Under that piercing gaze, Aika's feet faltered even more.
"Aika, you should stay a little longer. How about we have dinner together sometime? Even if I'm biased, my brother's cooking is actually pretty good."
"But I have a curfew..."
"A curfew?"
"U-um, yeah."
"What a shame."
What terrified Aika was that Marin wasn't saying this to provoke or tease her.
Yes, Marin genuinely wanted to share a meal. But deepening her friendship with Aika wasn't her true goal.
She was twisted too.
Marin loved Ryosuke—not as a family member, but as a man. She loved her older brother-in-law in the most genuine sense.
Aika hadn't heard this directly from Marin, and Ryosuke would never say such a thing.
But Aika was certain.
She wasn't particularly perceptive when it came to people's emotions, but she was certain about this.
Because... she was twisted in the same way as Marin. That's why she understood.
However, the nature of their distortions differed.
Marin carried the sinful burden of feeling inexplicably jealous at the mere thought of her beloved brother-in-law embracing and cherishing another woman.
That's why, not just today but often, she tried to stop Aika. She wanted to see—needed to be confronted with—Ryosuke and Aika's affectionate closeness. That's why she held Aika back.
Just earlier, for example.
She must have been wallowing in perverse pleasure, imagining the sex Ryosuke and Aika were having upstairs while she remained on the first floor.
I don't know what twisted her like this.
But she laughed so genuinely, so happily, at Aika's stories about Ryosuke.
That terrified Aika. It felt like a stark reminder that she herself might be just as deranged, sending shivers down her spine.
To be honest, I don't know the true extent of Marin's relationship with Ryosuke.
No.
Probably, there's nothing between them at all.
Marin was different from Aika in that respect. She must have wanted to love Ryosuke as a man, even while maintaining their sibling bond.
In that one aspect, Marin surpassed all other women.
She would never succumb to carnal desires. By remaining pure and staying closest to Ryosuke—just that alone made her a special existence that neither Aika nor any other woman could ever be.
...I could never compete with Marin.
Realizing this was what made Aika terrified of her. She wanted to flee this place as quickly as possible.
"...Sorry, Marin-chan. I'm going home."
But today, Marin wouldn't let her escape so easily.
"Hey, Aika-san."
Before Aika could turn around, Marin moved first, closing the distance between them.
"..."
Aika's center of gravity shifted. Trapped against the hallway wall by Marin's advance, she found herself cornered.
"W-what?"
"You have a boyfriend now, don't you, Aika?"
"Huh? Uh, well..."
The interrogation she'd endured from Ryosuke on the bed just moments ago was still etched in her body. Instinctively, a dull heat stirred in her abdomen.
"You're not actually dating him, are you? You don't even like him, do you?"
"Kazuki-kun and I, we're..."
"Call him Kazuki-san. Huh."
Her faint smile revealed nothing of her intentions. How much like Ryosuke she is. The thought sent a shiver down Aika's spine.
"Poor Kazuki-san."
"..."
"He probably thinks you're dating, right? To string him along like that is cruel. After all, you love your older brother, don't you, Aika?"
"O-of course!"
That's one thing I can't compromise on.
Even if it's against Marin.
But I don't intend to monopolize him. Competing with someone and pushing them aside is something Aika has always loathed.
There's no need for that.
As long as Ryosuke continues to love me like he always has, that's enough. It's fine even if I'm not the only one.
"I think your Older Brother would be happier if you actually dated him. It's for your own sake, Aika-san."
"What do you mean?"
"Exactly."
Aika leaned even closer. The shorter girl gazed up at her, her eyes shining with an eerie light. Aika wanted to look away, but she couldn't.
Those black eyes held a sinister glow.
So frightening, so uncomfortable—
Yet they resembled the gaze of the person she loved. Those eyes seemed to see right through to the most shameful depths of Aika's soul.
"You know how it is, don't you? If Aika-san were to become Kazuki-san's girlfriend, I'm sure your Older Brother would severely scold her. She'd be claiming to love him while secretly seeing another man? I don't think he'd ever forgive such a shameless little bitch."
"..."
My fingers stiffened, and I found it hard to breathe. She'd seen right through me, just as I suspected.
"Isn't that actually wonderful news for Aika-san?"
"I-I... I'd never do such a thing..."
"I heard from your Older Brother this morning. You were on a date with that guy today, weren't you? And then you slipped into his bed afterward, and he showered you with so much love, didn't he?"
Marin's fingertips brushed against Aika's abdomen.
"Oof—"
Even through the fabric of her clothes, a jolt of electricity seemed to surge through her.
The spot where Marin's fingers touched was the place where Ryosuke had loved her most deeply. Marin's fingers accurately pinpointed that still-tender area.
Marin tightened her grip. Aika's soft flesh yielded under the pressure.
"Ah, ah—"
"If you dated Kazuki-san, Aika, wouldn't you get even more affection? Go on lots of dates with him, let him be tender with you. If you tell your Older Brother about that, I'm sure—no. Absolutely, I think your Older Brother would love you even more fiercely."
"Ah! Stop—"
Marin leaned forward, bringing her nose close to the nape of Aika's neck.
"I can smell my Older Brother on you. From your skin, from your hair. Did he kiss you a lot? Did he stroke you? Weren't you incredibly, incredibly happy? Huh?"
Marin's nose brushed against the base of Aika's throat.
"Ugh..."
"I love you so much, Aika. So fragile, so stubborn... It's like he's looking right at me."
"Ah...!"
As Marin whispered in her ear, a perverse pleasure coursed through Aika's spine.
"Aika."
When she called her name and tilted her chin up, Marin's face was so close their lips almost touched.
"...Right?"
Marin leaned in even closer, bringing her lips nearer.
"...Ngh!"
Bracing herself, Aika squeezed her eyes shut.
But...
No matter how much time passed, nothing more happened.
Suddenly.
"Ah-ha! Ah-ha-ha! What, did you think I was serious? You idiot!"
Marin doubled over, laughing mockingly.
"We're both girls, right? There's no way we'd do that. For someone like you to be taken in so easily by a younger girl—Aika, you're such an idiot. Ahahaha!"
Her entire body burned with humiliation, radiating heat.
"Ugh... Ugh..."
Without looking back, Aika slipped on her shoes and stormed out of the entrance.
Behind her, Marin's voice rang out:
"Got that?! Think about it carefully—how can you make your Older Brother love you? You should know, right, Aika?!"
Unable to stop her body from burning, Aika ran until she was gasping for breath.
Still, the words she'd thrown out clung to her back like a curse, refusing to fade away.
*****
Two days later, Aika officially began dating Kazuki.
*****
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