Generally, yobai refers to the practice where a man secretly enters a woman's bedroom at night to have sexual intercourse. This custom was typically practiced by young unmarried couples and was once common throughout ancient Japan.
It should be noted that yobai is a practice of the past and is no longer part of contemporary Japanese society. However, tonight the practice of yobai is happening again, and more shockingly, the perpetrator is not a man, but a woman.
(It seems tonight Aishia-san and Charlie-san aren't doing it.)
Standing in front of Charlie's bedroom door, Kei felt both relieved and tense when she didn't hear intimate sounds from inside.
Over the past year, she had become quite familiar with their relationship patterns—not every night would the couple have sex. Usually, they did it routinely five days a week, but tonight was an unexpected break.
(This is my chance! I can't miss it!)
Clenching her small fist, Kei took a deep breath and pushed the bedroom door open.
Charlie was sitting on the bed reading a book in his hand, illuminated by the dim light of a portable oil lamp beside the bed.
"Aishia, didn't Est ask you to sleep with her because she's been unhappy sleeping alone lately..."
Charlie stopped mid-sentence when he saw who entered. He, who possessed Six Eyes with extraordinary vision capability, caught every detail of Kei's appearance in the dim oil lamp light.
Kei was wearing a very thin white sleeveless shirt. The shape of her breasts was clearly visible behind the fabric, with protrusions in the middle indicating she wasn't wearing a bra. Her long legs were clearly displayed, as she only wore dark-colored hot pants.
"Gulp..."
Charlie couldn't help but swallow. After months of enjoying Aishia's body in various variations, his resistance to female temptation wasn't as high as before.
"Charlie-san..."
Seeing his reaction, Kei became more confident. She walked closer, her cheeks flushed, her breathing beginning to pant. The fresh scent of a young girl mixed with a slight smell of sweat filled the room.
"Wait a minute, Kei! What are you trying to do? Calm down, don't be rash!"
Realizing the anomaly in the girl—Kei was clearly acting out of character—Charlie panicked slightly, putting the book beside him. However, it was too late; Kei quickly pushed him back onto the bed, then sat on him. Her position allowed her to feel the warmth of the girl's body through the thin fabric that barely covered anything.
"Kei! What's wrong with you?! Did you eat something wrong?! Come to your senses!"
Charlie tried to hold her shoulders as she was about to lean down to kiss him.
"This is all your fault, Charlie-san! You're the one who made me like this! You have to take responsibility!"
"Huh? My fault?"
Charlie was truly confused. He didn't understand where his fault lay.
The sexual frustration that had been accumulating for so long now exploded into a series of emotional accusations. Kei expressed the thoughts she had been keeping in her heart.
"Yes, your fault! Almost every night! For over a year in China and now in Indonesia! I've been hearing it, Charlie-san! I hear it every night! Aishia-san's moans, your gasps, the sound of your bodies colliding... How could I not be affected?"
Hearing that, Charlie was stunned, his eyes widening.
"You... you've been listening to us? Kei, I... I didn't know—"
"Of course you didn't know!" Kei interrupted. "You were too busy with Aishia-san to realize there was someone else suffering because of you two!"
"Anyone in my position would feel the same! Every night I get aroused! I have to masturbate until my body hurts just to be able to sleep!"
"I'm only human, Charlie-san! I'm jealous! I'm jealous of Aishia-san who can be with you! You destroyed the boundaries I've been maintaining! You ruined the last innocence I had!"
Tears finally flowed down Kei's cheeks.
"I've tried to release it myself, but it's not enough! Never enough! I can't hold it anymore. Tonight, I came here not to peek. I came here to stop this frustration!"
"..."
Charlie fell silent, stunned by the confession that was so honest and full of emotion. He just realized how selfish he had been all this time, too focused on his own comfort without thinking about the feelings of the young girl living with them.
"You're still too young, Kei. I promise I'll install soundproofing next time."
Neither agreeing nor disagreeing, Charlie tried to buy time. His voice sounded gentle yet firm, holding onto reasons of morality and law.
A flash of anger, frustration, and disappointment crossed Kei's blue eyes.
"Too young?" Kei laughed cynically, her tears beginning to pool. "Charlie-san, do you know? At midnight tonight, I'll turn exactly 18 years old. Legally I'm old enough to marry! Besides, what kind of law still applies in a world with only three humans left?"
She took a deep breath, her voice trembling but clear.
"Tell me, Charlie-san. Do you hate me so much that you reject me like this? Am I that unattractive? If so, I'll leave. I'll leave Charlie-san's side tonight, and I'll never appear again. I'll find a way to live alone, as I should."
Faced with the girl's sad and pleading gaze—a gaze that now implied a serious threat to run away and disappear forever—Charlie sighed deeply, raising the white flag in his heart.
He released his grip from her shoulders.
(That's enough. This girl has shown her determination this far. If I keep refusing, I'm no different from Rio and other loser harem protagonists I've always looked down on. At worst, I'll use my Quest reward to bring Kei to the Danmachi World.)
While Charlie was silent, immersed in his calculations, the blue gleam in Kei's eyes slowly dimmed. She thought the other party had definitively rejected her. His silence felt more painful than words.
"I see. So this is what rejection feels like." She whispered, her voice barely audible. "Indeed, compared to Aishia-san's world-class beauty, I'm nothing."
Filled with piercing disappointment, Kei held back the tears that wanted to burst out. With slow movements full of anguish, she got down from Charlie's still-silent body. Her small feet touched the cold floor, and she turned to leave the room—to go as far as possible, as she had said.
But just as she took her first step, a warm and strong hand suddenly grasped her delicate wrist.
"Wait. I don't hate you, Kei. I'm just... worried you'll regret this decision." Charlie's voice finally broke the silence.
Kei turned around, her teary eyes now filled with vulnerable hope.
"I've been thinking about this for months, Charlie-san. I know what I want."
Charlie sighed, this time with a small surrendering smile.
"In that case... happy birthday, Kei."
He pulled the girl back into his embrace, this time without hesitation. His large hand gently caressed Kei's white hair, which was as smooth as silk.
"I won't let you go. I don't hate you, Kei. It's because I care that I want to make sure you're not doing something you might regret later."
"Your age may be legal now, but I want you to be sure of this decision. This isn't about comparing you to Aishia; you're beautiful in your own way."
Kei sobbed, a mixture of relief and confusion.
"So... Charlie-san isn't rejecting me?"