"When are you going to the department store today, sis?"
While masturbating with her panties, Jinwoo asked Sohee, who was showering.
"Yeah~ I'll be leaving around 11, so get ready~"
Sohee's reply came from the other side of the frosted sliding glass door of the bathroom.
Under normal circumstances, with their mom at home, it would have been taboo for Jinwoo to enter the changing room while Sohee or Minji was showering.
The strict household rules that had been implicitly upheld in Jinwoo's home were now being trivially broken.
The casual conversation with Sohee was providing a significant stimulus to Jinwoo.
Jinwoo evenly spread the fluids from the blue striped panties Sohee had taken off over his erect penis.
The slippery touch of Sohee's fluids and the soft fabric Jinwoo was now wrapping his enormous penis with Sohee's damp panties, moving them up and down to create friction.
A sweet and mysterious pleasure seemed to spread from Jinwoo's genitals throughout his body.
"Do you want to go out for lunch?"
Jinwoo, seeking to hear more of Sohee's voice, intentionally started a conversation while masturbating.
"Yeah, I'll buy you lunch~"
Sohee, who had just gone to shower, could not have missed the traces Jinwoo had left all over her clothes in the basket and the pervasive male scent filling the changing room.
The conversation between the recently masturbated younger brother and older sister, separated only by the glass door, might have been awkward, but Sohee was continuing as if nothing was amiss.
Sohee knew that her naked silhouette was visible to Jinwoo through the frosted sliding glass door.
The tacit complicity in their deviant acts seemed to be increasingly dulling their rational thoughts about reality.
* * *
"Jinwoo, you haven't been to the aquarium at the department store yet, have you?"
"No, I've never been. Have you, sis?"
"I've been there a few times after school~"
"Alone?"
"No~ with friends~ It has a really nice atmosphere."
"Really?"
"Yeah, after we eat lunch, we can watch a movie and stop by the aquarium before heading home. We'll have plenty of time, so we can also look around the shops~"
Sohee was simply outlining the day's plans she would be spending with Jinwoo.
* * *
While continuing to masturbate and converse, Jinwoo, glimpsing Sohee's enticing movements as she bent over or crouched beyond the frosted glass door, imagined her swimming naked in the aquarium.
"Sohee sis, how's that thing you were supposed to do with Sinbi noona going?"
Jinwoo brought up a previous conversation he remembered where Sinbi had come over and they had seemingly excluded him while chatting.
"What? Which one?"
"That time Sinbi came over and you guys were eating ramen together. Was it about a diet?"
Jinwoo, aware of what the sisters had discussed from hearing it from Sinbi, pretended to be clueless to probe Sohee.
"Oh? Ah~ yeah, that's right~."
Sohee answered, somewhat evasively.
It seemed like she roughly understood what Jinwoo was talking about.
Unlike before, when she had been quite curt with Jinwoo, Sohee's attitude towards him had softened considerably.
* * *
Jinwoo momentarily imagines a scene where he is having sex with Sohee to help with her diet.
He pictures pulling her wet body straight out of the aquarium waters, laying her down face-first, and climbing on top to forcefully penetrate her as if assaulting her.
Then, he starts to thrust relentlessly and vigorously without pausing or climaxing.
A dominating and violent sexual violation.
Imagining the moans Sohee emits while pressed under his body sends a tingling pleasure coursing through him, almost bringing him to climax.
"Sis, you look so good right now, you don't seem like you need to lose any weight at all."
Jinwoo, eyes fixed on the silhouette of Sohee's body through the frosted glass, says while increasing the speed of his strokes.
The sound of flesh slapping against his groin begins to be barely audible.
Thud!
Thud..
Thud...
After a brief silence, Sohee speaks up.
"If you're not careful, you gain weight quickly~. You know how mom always makes sure we eat regularly at home."
"Really?"
"Yeah, because of mom, I can't even think about dieting by starving."
Jinwoo smiles slightly at Sohee's cute excuse.
He remembers the dessert cafe in front of Sohee's school they had visited before.
-The lascivious Sohee who indulges while making sincere excuses-
"So, have you and Sinbi decided to go on that diet?"
"Not yet~"
"Does it actually work?"
"Well..? From what I hear from those who are doing it, it doesn't seem too bad..."
"Do many of your friends do it?"
"Uh.. yeah... But why are you so interested in my dieting?"
Sohee sounds slightly annoyed by Jinwoo's interest in her diet.
"No, I just want to help out Sohee sis if I can~"
"Ha- Do you even know what that entails?"
Sohee scoffs and asks Jinwoo.
"Whatever it is, it's something we'd do together, right?"
As he says this, Jinwoo speeds up the hand gripping and shaking his penis.
Thud!
Thud!
Thud!
The sound of flesh slapping was gaining momentum, echoing inside the changing room, faint enough that it might or might not reach Sohee.
Jinwoo was masturbating secretly, nervous about possibly being caught by Sohee, yet part of him hoped she would notice.
He had a vague expectation and confidence that even if Sohee caught him today, she would not get angry and would let it pass.
There was a pause in conversation from Sohee again.
"We haven't decided yet~ I still need to talk more with Sinbi... And anyway, it's something you can't do with us, Jinwoo."
Sohee seemed to be setting boundaries with Jinwoo.
"Why?"
"It's just how it is~!!"
Through the conversation, Jinwoo had finally confirmed that the diet Sohee and Sinbi were planning was indeed the one he had heard about.
Jinwoo had once received confirmation from Sinbi by writing "SEX" on her palm as a correct guess, earning himself a reward, yet a part of him had always harbored a sense of disbelief.
Perhaps there was a part of him that hoped it wasn't true.
"Sinbi could easily play such a prank on you."
"I don't think it would bother me?"
Jinwoo probes again.
"Ha- Jinwoo, do you even know what you're talking about?"
Sohee scoffs, speaking to Jinwoo as if he's clueless.
"Anyway, it's with Sohee sis, I think anything would be okay with me."
Jinwoo, conscious of sex, was speaking to Sohee.
* * *
Seeing Sohee's panties soaked with her fluids, Jinwoo realized that Sohee was sexually responsive to him.
He felt validated as a male by Sohee.
In such a situation, the thought of Sohee being with another man was intolerable to him.
Jinwoo stroked his penis vigorously, as if to show off his strength.
Creak Thud! Thud!! Thud!!! Thud!!
The changing room was again filled with the sound of the shower leaking from the bathroom and Jinwoo's masturbation.
Sohee was possibly feeling something too, as she was now silent and motionless.
Standing in the shower, naked, Sohee listened to the sounds of her younger brother masturbating.
A long silence ensued.
Soon, Jinwoo felt the rush of climax approaching.
Among Sohee's clothes on a side table, the green shell-shaped bra that Jinwoo had noticed earlier caught his eye.
Quickly, he grabbed the green bra and brought it in front of his glans.
He then faced towards where Sohee was, performing the final vigorous thrusts needed for climax.
Thud Thud Thud Thud Thud~!!
"Ugh... Hmm Ah~"
Jinwoo moaned as he began to climax.
He released his semen abundantly into the green shell-shaped bra that Sohee had worn.
A refreshing second climax without any feelings of guilt, embarrassment, or emptiness.
It seemed that Sohee had planned to wear the bra again after her shower, as she had left it on the side table instead of the laundry basket.
What would Sohee's reaction be if she saw what Jinwoo had done to the bra she had temporarily taken off?
Jinwoo carefully placed the bra back into the laundry basket.
Then, as if nothing had happened, he silently exited to the living room.
Jinwoo was about to start another day just like that.