When I was dating my wife, her younger sister was already a sophomore in college.
Because I've been clingy to my sister since childhood, she often gets stuck in the middle as a third wheel, making me afraid to move my hands freely, worried she'd see me being intimate with my wife and go out gossiping.
Time passed quickly. Several years later, I finally got married, moved into my own new home, and thoroughly enjoyed the world of two. And my sister-in-law had long since grown from a naive college student into a mature young woman.
The sisters' bond remained strong; she would often come to my house to play with her sister. After the honeymoon phase passed, in my spare time, I would also observe her increasingly voluptuous figure. She wasn't tall, less than 1.6 meters, petite and adorable, but her breasts had developed quite well. Through intentional or unintentional physical contact, I had long been aware of this.
Soon, my wife became pregnant. We both love children, so we agreed to do that less often. But the fire of desire in my heart was hard to calm, and my gaze unconsciously fell on my sister-in-law.
Actually I could feel that she wasn't completely indifferent to me either. She would secretly glance at me with her eyes, lightly brush against my body when walking, and when we walked together she would even unconsciously hook her arm around mine. I used to think of her as my sister-in-law and didn't think too deeply about it. Now it's different. I haven't touched my wife for several months, and my desire has built up badly. There is only one thought in my mind — possess her.
That day, my wife went to the hospital for a prenatal checkup, and I was doing housework at home. The doorbell rang. I opened the door to see my sister-in-law. She had brought a few CDs my wife liked from home, saying they were for the future baby's prenatal education.
I took the plate and placed it next to the TV, invited her to sit, and went to the kitchen to make coffee. Then I found out there was no coffee left—she really likes it, and I always make her some when she visits. I had to let her watch the DVD first while I went downstairs to buy some.
Only when I reached downstairs did I remember: mixed next to the DVD player were two adult films and one softcore film. I inwardly exclaimed in alarm—if she saw them, my image as her brother-in-law would be ruined. I hurried back.
When I got home and opened the door, it was already too late.
My sister-in-law was sitting on the sofa, with a plot-based Japanese AV playing on TV. The man and woman in the film were still in the flirting stage. I quickly grabbed the remote to change the disc, but she firmly refused, blushing and saying, 'I'm not a child anymore; watching can also teach me something.'
Helpless, I had to brace myself and sit down to watch with her.
On the screen, the man and woman quickly undressed and entered the deep stage. The man teased the woman's ears, neck, and breasts with his tongue, then moved lower. The woman kept moaning with pleasure. I stole a glance at my sister-in-law; her face was completely flushed, her legs clamped tighter and tighter, her body unconsciously squirming.
I quietly moved closer to her.
At that moment, the phone rang. My wife called, saying she had run into a female classmate and wouldn't be home for dinner that night.
Now I'm completely relieved.
After hanging up the phone, I hesitated no longer and reached out to pull her into my embrace. She struggled briefly in the throes of desire before finally softening. I lowered my head to kiss her, and she instinctively clenched her teeth. I slipped my hand under her top, found her nipple through her bra, and gently pinched it. She let out a soft 'oh,' and I seized the moment to slip my tongue inside.
The virgin's body scent continuously stimulated me. While kissing her, I unfastened her bra from behind. Her B-cup breasts were fully exposed. I used my fingers to knead her nipples, then turned to kiss her earlobes. Soon, she was completely lost in lust, her resistance gone.
I pushed her top up and lowered my head to gently suck her nipple. The early summer weather wasn't hot, but she had a fine layer of sweat, her breasts carrying a faint salty taste. I was already painfully hard; I took off my pants and guided her small hand to hold me.
It was her first time touching a man's thing, and she was so nervous she didn't know what to do. Blushing, she said: "Brother-in-law... this thing is so big... mine is so small... no more... I'm scared..."
I didn't give her a chance to refuse, lifted her skirt, pulled down her white panties, and lowered my head to kiss that spot. Her nearly hairless pussy, with only sparse pubic hair, was full and tight, no odor, just a fresh body scent. I licked and sucked desperately; she soon moaned continuously, pleas for mercy also coming one after another.
The lower part was already overflowing. I pressed the glans against the entrance and gently rubbed the clitoris. She had never experienced such stimulation; before long she reached her first orgasm, and a torrent of love juice gushed out.
I aimed at the entrance and forcefully sank my body down.
A virgin's body was indeed different. The tight vaginal walls tightly wrapped around, making it difficult to advance even just the glans. I dared not act rashly, leaning down to take her nipple into my mouth again, sucking while gently rotating my lower body. After she adapted, I held her waist and began shallow thrusts. When advancing to about one-third, I encountered an obstacle—that was proof of her virginity.
I took a deep breath, gripped her slender waist, and thrust hard.
Immense pleasure and the pain of losing her virginity struck simultaneously. She opened her mouth to cry out, I immediately kissed her, turning the cry into a muffled groan. I closed my eyes, enjoying the feeling of that tight, sucking embrace, the vagina constantly contracting, sucking like a little mouth.
Under continuous caressing, the pain gradually faded, replaced by waves of aching itchiness. She looked at me shyly, wrapped her legs around my waist, and began to twist her lower body. I deliberately remained still and softly asked, 'What's wrong with you?'
"Brother-in-law... the area down below feels strange... it hurt a lot just now, but now it doesn't hurt much; it's a bit numb and itchy..."
"Then is brother-in-law not moving anymore?"
She grew anxious: 'Can you just move a little... you're so big there, stretching me so full...'
I started thrusting nine shallow and one deep. For her, who had just lost her virginity, this rhythm was most suitable. Soon she was panting and moaning, lost in ecstasy: 'Mmm... brother-in-law... I love you... I'll be with you forever...'
To completely possess her body and mind, I deliberately pulled out and stopped at the opening. She had become addicted to the taste and kept twisting her butt to come up and meet me. I asked teasingly: “What do you want to do?”
“You… come in…”
I vigorously kneaded her breasts, my lower body thrusting deep to the hilt. The pleasure of the glans scraping past her cervix was intense. She completely surrendered, wrapped her arms around my neck, and whispered in my ear, 'Brother-in-law, from now on you are my husband... I will love you forever.'
I stopped holding back, thrusting hard while training her. Made her say 'fuck my cunt,' say 'master,' admit she was a sex slave. At first she was shy, but later fully cooperated, softly moaning: 'Master... this little slut's pussy is so itchy... please use your big cock to help your slave...'
I thrust vigorously over a hundred times, releasing in a torrent as we climaxed simultaneously, shooting all the semen accumulated over three months into her tight, hot body.
After a few minutes, I was about to get up, but she wrapped her legs around my waist and whispered: 'Master... your slave feels so good... wants to be connected as one with Master forever...'
After hearing this sentence, my desire rose again. Using the lubrication from before, I began a new round of thrusting and training.
From that day on, my sister-in-law became my secret sexual partner.
When the wife was at home, we pretended to be ordinary sisters and brother-in-law; when the wife wasn't there, she would actively send messages or come directly to my place. Each time was more uninhibited than the last. She learned various positions, learned to moan wantonly beneath me, and also learned to clamp her legs tight after climax, not letting me withdraw immediately.
On the surface, she still came to see her sister, deliver things, and help with household chores, but as soon as my wife was not around, her gaze would change. Sometimes she would deliberately wear something shorter and tighter, swaying her hips slightly when walking; sometimes she would find an excuse to walk behind me, brushing her chest against me almost imperceptibly.
At first, I pretended not to know, but later I simply stopped hiding it.
Once my wife went to the maternity center for a prenatal class and wouldn't be back until afternoon. My sister-in-law came at noon. As soon as the door closed, she pressed me against the entryway and kissed me. The kiss was urgent, her hand already in my pants. I carried her to the sofa, lifted her skirt, and found she wasn't wearing underwear inside.
"On purpose today?" I asked.
She nodded, blushing, and spread her legs herself: "Missed you... missed you these past few days."
I lowered my head and kissed her, using my tongue to wet her, then entered fully. She was much more relaxed than the first time, still tight and hot inside, but she actively lifted her hips to meet me. I thrust deep and hard, she bit the back of her hand to suppress her cries, afraid the neighbors would hear. When her climax came, her whole body tensed, her inner walls contracting in waves, squeezing me until I came too.
Afterward she lay on my chest, her voice still a little breathless: "Brother-in-law... when your wife isn't around, can you call me over more often?"
I pinched her nipple: "Take the initiative yourself."
She gave an 'Mm' and buried her face even lower.
Then she really took the initiative.
Sometimes in the afternoon, a sudden message: 'Sister went to the hospital, I'm coming over.'
Sometimes after my wife falls asleep at night, she would tiptoe over from the guest room and slip under my covers. We try not to make noise, but once we truly enter, suppressed gasps still escape. She learned to call me 'Master' in a breathy voice beneath me, learned to keep her legs tightly together after being filled inside, learned to use her mouth to get me hard again.
My wife's belly grew bigger and bigger, and her movements became increasingly inconvenient. Our sex life almost completely stopped. The suppressed desires were all poured onto my sister-in-law. She came more and more frequently, sometimes three times a week, sometimes two days in a row. Every time before leaving, she would carefully cover up any marks on her body, change into ordinary clothes, and revert to being the good little sister who just came to see her sister.
But once the door closed, she was someone else again.
One night she came with a slight smell of alcohol.
"A class reunion, I had two drinks." She explained, then knelt down directly and took me into her mouth. Her technique was much better than at first; her tongue skillfully circled the tip, occasionally going deep-throat. I pressed the back of her head, making her take it deeper. She didn't resist, instead letting out satisfied muffled moans. Just as I was about to cum, she pulled back and looked up at me:
「Inside.」
I pulled her up and pressed her against the wall to enter her. This time was especially rough. Her legs were wrapped around my waist, and each time I thrust to the deepest point, she let out a short cry. When her climax came, her whole body tensed, her insides gripping me tightly. I bit her shoulder and came inside her completely.
Afterward she leaned against me, her breathing not yet steady.
"Is it really okay like this?" she suddenly asked.
I was silent for a while.
"Do you want to stop?"
She shook her head, burying her face in the crook of my neck: 'I don't want to. It's just... occasionally I get scared.'
I held her tighter.
Outside the door were the lives each had to maintain—she had studies, parents; I had a wife, a child about to be born. Inside the door, however, was another set of rules, where we could do as we pleased, scream as we pleased, and release the desires accumulated during the day over and over again until they were completely spent.
And we all know that as long as we want to continue, no one will be the first to say it's over.
In the month before my wife's due date, my sister-in-law came over almost every other day.
Sometimes it's daytime, curtains drawn tightly, sunlight only leaking through the gaps; sometimes it's late at night, not stopping until her legs are weak. She started actively asking for more positions—being entered from behind, being pressed against the floor-to-ceiling window, having her wrists tied. I satisfy her every time. After each internal ejaculation, she would keep her legs tightly together for a long time, as if trying to keep everything inside.
The day the child was born, the younger sister-in-law was also at the hospital.
She held her sister's hand, her eyes red. I stood to the side, watching the sisters lean on each other, but in my mind flashed those secret scenes—her moaning beneath me, her dazed expression after being creampied, the way she willingly knelt down to take me in her mouth.
Once desire is ignited, it is difficult to extinguish.
And that door had long since been flung wide open.
Can’t be closed anymore.
After the child was born, the household became completely chaotic.
My wife is in her postpartum confinement. During the day, a confinement nanny takes care of her, but at night, someone often needs to soothe the baby. I am nominally a responsible husband and father, but in reality, I spend more energy figuring out how to see my sister-in-law.
She was more careful than before.
When coming over, she would send a message in advance to confirm that my wife was asleep and the postpartum caregiver wasn't in the living room. Sometimes she only stayed for half an hour, sometimes she could steal one or two hours. Every time we met, she seemed like she had been starving for a long time; as soon as she entered, she would pounce on me to kiss me, her hands urgently unbuttoning my pants.
"These past few days... I've been missing you to death." She buried her face in my neck, her voice trembling.
I pressed her against the wall and entered from behind. She bit her own hand, trying hard not to make a sound. Inside, she was wetter and hotter than before, each thrust producing faint, wet sounds. I reached around to the front and rubbed her clit. She soon tensed up, her inner walls contracting violently. I didn't stop, continuing to thrust to the deepest point until I also came inside her.
Afterward she clamped her legs tightly together, not letting the semen flow out, and leaned against me, panting.
“Next time... can it be longer?” she asked quietly.
I pinched her nipple: "Depends on the opportunity."
Opportunities always exist.
During her postpartum confinement, my wife had limited mobility and often slept a lot in the afternoon. My sister-in-law would use the excuse 'to see my sister and nephew' to come over, but in reality, she spent most of the time entangled with me in the guest room or master bedroom. Once, we were in the middle of it when the confinement nanny called from outside the door. She was so scared she froze completely, but her inner walls clenched even tighter. I covered her mouth and slowly continued thrusting until she climaxed again in extreme tension.
That kind of stimulation became addictive for her.
After that, she began actively asking for more stimulating settings—on the sofa in the living room, on the kitchen counter, and even once on the balcony (with the curtains drawn tight). After each internal ejaculation, she would clamp her legs together for a long time, as if she wanted to lock everything inside her body.
On the day the child turned one month old, many relatives came to the house. My sister-in-law was also there. She held the child, smiling very gently, sitting and chatting side by side with her sister. I stood nearby socializing, but my peripheral vision kept drifting towards her. She occasionally looked up at me, a flicker of meaning in her eyes that only I understood.
After seeing off the guests in the evening, my wife was exhausted and went to bed early. My sister-in-law proactively stayed behind to 'help.'
As soon as the door closed, she pulled me into the guest bedroom.
This time she was especially proactive. She took off her clothes herself, straddled me, and guided me as she slowly lowered herself. When she reached the deepest point, she let out a soft gasp, then began to move up and down on her own. I held her waist, watching her intoxicated expression, occasionally reaching up to knead her breasts. Her movements grew faster and faster, and she soon climaxed, her inner walls clamping down tightly on me.
I rolled over and pinned her beneath me, continuing to thrust. Her legs wrapped tightly around me, actively meeting my movements, her voice suppressed yet wanton: 'Master... deeper... shoot inside...'
I satisfied her. After shooting everything inside, she clamped her legs tightly shut, looking at me with dazed eyes.
“I think... I’ve kind of fallen in love with this feeling.” She said softly.
I didn't answer, just pulled her into my arms.
And so the days passed one by one.
As the child gradually grew older, my wife recovered almost fully, and our sex life slowly resumed. But the things between me and my sister-in-law didn't decrease at all. She learned to talk to me nonchalantly during family gatherings, learned to act obediently in front of her sister, and also learned to completely let go when it was just the two of us.
Once she stayed overnight at my place.
At night, the child cried and fussed, my wife went to soothe him. She quietly slipped into the master bedroom and lay down beside me. We tried our best not to make a sound, but when I entered her, she still let out fragmented whimpers. I covered her mouth with my hand, thrusting deep again and again. She climaxed under extreme suppression, her body trembling violently, her inner walls contracting in waves.
Afterward she whispered in my ear: “Next time... I want to be tied up.”
I agreed.
Once desire is ignited, it is difficult to extinguish.
And that door had long since been flung wide open.
Can’t be closed anymore.
The story is still continuing.
Each time she pushed open the door, each time we locked the door, it felt like confirming the same thing—
Some boundaries, once crossed, can never be returned from.
Each time she pushed open the door, each time we locked the door, it felt like confirming the same thing—once certain boundaries are crossed, there's no going back.
When the child was six months old, the family finally felt a bit more relaxed. My wife started taking the child out to get some sun and participate in mom group activities, often not being home during the day. My sister-in-law seized these gaps and came over more frequently.
Sometimes it was in the morning, she would use the excuse of delivering something; sometimes it was in the afternoon, directly sending a message: 'Are you free now?'
I replied, "The door isn't locked," and she would appear within twenty minutes.
As soon as she came in, she was often already wet. Once she was wearing a skirt, with nothing on underneath, and directly pinned me down on the sofa, then climbed on top herself. When I reached the deepest point, she let out a satisfied sigh and then started rocking herself. I held her waist, watched her intoxicated expression, and occasionally reached out to rub her breasts or clitoris. She quickly climaxed once, and her inner walls clenched so tightly that I almost wanted to cum immediately as well.
I held back, turned her over, and entered from behind. She buried her face in a pillow, trying to keep her voice down, but each time I thrust deepest, a whimper would escape. I reached around to the front and quickly rubbed her clit. She soon climaxed again, her body shaking violently. Only then did I speed up and shoot everything inside.
Afterward she lay still, with semen slowly trickling down her thigh. I helped wipe her clean, but she suddenly grabbed my hand and put it back between her legs:
"One more time... I want it."
I got hard again, this time having her lie on her back with her legs over my shoulders, entering her deeply and slowly. She looked into my eyes and voluntarily said things she usually wouldn't dare, calling me 'Master' and saying she was 'a sex slave belonging only to brother-in-law.' Those words excited me more than ever, and in the end, I came copiously and deeply.
She kept her legs tightly closed for a long time before finally relaxing them.
“I think I really can’t live without it anymore.” She said softly.
I didn't respond, just kissed her forehead.
The days slipped by like this.
On the surface, we were still just an ordinary brother-in-law and sister-in-law. At family gatherings, she would help her sister take care of the children, talk to me normally, and occasionally even deliberately joke in front of others, saying, 'Brother-in-law is so good to sister.' No one noticed anything unusual.
But only we know what the scene is like behind the door that’s locked from the inside.
Once she came to stay for the weekend.
At night, the child was asleep, my wife was also asleep. She slipped into my room and got under the covers. We had almost no foreplay; she was already soaked, I entered directly. She buried her face in my chest, suppressing all sounds, relying only on her body's reactions to tell me how much she was enjoying it. When she climaxed, her whole body tensed, her nails digging into my back. After I came inside her, she still kept her legs tightly together and whispered:
"Don’t come out... stay a little longer."
I obeyed her.
After a long time, she finally let go, got up, and prepared to return to the guest room. Before leaving, she glanced back at me with a complex look in her eyes:
"If one day... elder sister finds out?"
I remained silent.
She shook her head herself and smiled: 'Forget it. I don't want to think about these things.'
The door was gently closed.
I lay in the darkness, listening to her footsteps fade away, knowing in my heart—this door had opened too completely, and it could never truly be closed again.
It took a long time before she let go and stood up to return to the guest bedroom. Before leaving, she glanced back at me, her expression complicated:
"If one day... elder sister finds out?"
I remained silent.
She shook her head herself and smiled: 'Forget it. I don't want to think about these things.'
The door was gently closed.
I lay in the darkness, listening to her footsteps fade away, knowing in my heart—this door had opened too completely, and it could never truly be closed again.
The desire is still burning.
And the story was still continuing.
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