ONYX FICTIONAfter sibling incest, I became my brother's sex slave: from gender transformation to being penetrated to climax, my womb filled with semen.
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After sibling incest, I became my brother's sex slave: from gender transformation to being penetrated to climax, my womb filled with semen.

♙ Anonymous◷ 2026-08-19◉ 0
University Student

A failed exam candidate, after accidentally transforming into an adult woman via a mysterious drink, starts anew at university with a new identity. With her younger brother, also a university student, they gradually cross the boundaries of blood within the cracks of campus and family life, developing a secret yet profound entanglement of flesh and emotion. The story revolves around adaptation to adulthood, taboos, and descent.

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It happened on the day my university graduation results were announced.

After the list was released, I didn't even get into the worst school. Walking on the streets of Taichung, I felt completely drained. In a few months I might have to go to the military, and my future was blank. In that state of confusion, I walked in front of a rundown convenience store. An old grandmother outside suddenly stopped me and said, 'Kid, you look very down. Come in, Grandma will treat you to a drink.'

At the time, I was practically half-dragged, half-pushed into the shop by her. The proprietress handed me a drink, saying that if I drank it, those troubles would disappear. I don't know if it was because I was disheartened or if the drink itself carried some indescribable power, but I drank it almost without hesitation. Afterward, my consciousness grew increasingly fuzzy, my body gradually lost strength, and I finally lost consciousness completely.

When I woke again, it was already dark. I was lying in the pavilion in the park, completely confused. A urge to urinate forced me to stand up and look for a toilet. When I walked to the washstand, the figure reflected in the mirror made me freeze—my already slim and delicate self now looked even thinner, my face soft to the point of almost not seeming male.

Entering the bathroom, I unzipped my pants to relieve myself when I realized what should have been there was gone. In its place was a thin slit. Looking down at my chest, the outline hidden by my clothes was unmistakably a pair of full breasts. I froze on the spot, my heart pounding so fast it felt like it would explode.

I hurriedly straightened my clothes, my mind in chaos, and could only head home first.

As soon as I entered, the whole family was there. Dad, Mom, my sister who was about to get married, and my second younger brother who was already an adult (19 at the time, and like me, preparing to go on to higher education), all wore shocked expressions. I told the whole story from beginning to end. Everyone stayed silent for a long time. That dinner was unusually quiet.

Over the next month, the family tried every method possible—hospital examinations, prayers, divination—but none of it worked. In the end, my parents had no choice but to go to the district office to handle the relevant changes to the records, and formally announced at a family meeting: from now on, the old me no longer existed, and in my place was “Jiajuan,” the family’s new member. Everyone still had to live together well as family.

The next day, my mother and sister took me to the department store to buy women's clothing and supplies. When measuring my figure, I truly realized that my physical condition after becoming a woman was quite good: about 158 cm tall, weighing 45 kg, with approximate measurements of 33C-24-34, and my skin had also become much smoother. After returning home, they began teaching me feminine posture, dressing, and daily life details. At first, it was very uncomfortable—wearing skirts, bras, softening my speech, and restraining my movements. But after two months, I gradually adapted. Mentally, I had come to see myself as a woman about eighty percent of the time.

I decided to start over with a new identity, enrolling in university retake cram school. My younger brother was also preparing for entrance exams at the same time. We often went to cram school together; on the surface, we were just ordinary siblings, but in reality, I was already living fully as a woman.

After getting into university, I chose a private university not far from home, majoring in Applied Foreign Languages. My second brother got into the Business School of the same university. Since home wasn't far from school, neither of us lived on campus, commuting daily. This actually gave us more time alone together.

About half a year after becoming female, I began to notice something was wrong.

Underwear and panties would vanish without a trace, then reappear inexplicably a few days later; when taking a shower, I vaguely felt someone lingering outside the door; when sleeping, I occasionally felt someone touching my body. At first I thought I was just overthinking it, until one time I accidentally caught my second brother masturbating with my underwear, and only then did I fully understand.

We originally slept in the same room (due to limited rooms at home). I didn't react immediately, just kept it in mind. Until one day when only the two of us were at home, I walked into the room and happened to see him going through my closet again.

I sat by the bed, asking him in as calm a tone as possible:

"Do you have a girlfriend now?"

He was obviously nervous, and stammered that he didn't.

I got straight to the point: 'I used to be a boy too, so I probably know what kind of curiosity you have at this age. I know about you taking my underwear and touching me at night. I'm not blaming you, but you have to be honest.'

Second Brother was silent for a long while, and in the end admitted it with his head lowered. He said that when I was still male, he hadn’t behaved this excessively, but ever since I changed into my current form, he often couldn’t restrain himself.

I looked at him, feeling somewhat conflicted. Finally, I said, 'It's fine if you take the underwear, but you have to wash it clean and return it. And from now on, no more secretly touching them while sleeping, understand?'

He nodded repeatedly.

Just as I wanted to lie down and rest, he suddenly spoke again, his voice carrying obvious tension and mustered courage:

"Sis... you used to be a man, so you should know I'm very curious right now. Could you... let me take a look at a woman's body? Just look, please."

I was taken aback and instinctively wanted to refuse. But seeing his expectant yet somewhat fearful-of-being-scolded expression, coupled with my own vague curiosity and an indescribable excitement, I finally nodded.

“Only look. Don’t touch.” I emphasized.

He immediately agreed.

I began taking off my clothes one piece at a time. When my top came off, revealing my braless chest, he clearly gasped, his gaze turning sharp. Then came the pants. Finally, only my panties remained. He suddenly spoke: 'The last piece... could I help you take it off?'

Before I could answer, he had already crouched down and reached out to pull down those panties.

The air instantly became both quiet and scorching.

I stood completely naked in front of him, his gaze fixed intently between my legs. I felt somewhat embarrassed, reaching out to cover myself, but he gently brushed my hand away. He suddenly said, "Then I'll show you too." After saying that, he quickly stripped completely naked. His genitals were fully erect.

Whether it was out of curiosity, or because I had once been male myself and was not unfamiliar with that kind of thing, I reached out and grasped it, slowly stroking it. Later, I even lowered my head and took it into my mouth.

He was obviously very nervous, but he didn't push me away. I used my tongue to circle and lick the tip, then took the whole length into my mouth, moving back and forth. Before long, he suddenly gave a low gasp and came. Most of the warm liquid went into my mouth, and I swallowed it reflexively, with some still left at the corner of my lips.

I wiped my mouth and complained with a bit of a pout, asking why he didn't tell me earlier. But he pulled me back, saying he hadn't seen enough.

I couldn't resist him, so I stood there letting him continue looking. Just as I asked, "Have you seen enough?" he suddenly pounced, pushed me onto the bed, and started kissing and touching me again.

“Little brother, you can’t... we agreed to only look, not touch...” I tried to push him away, but I was clearly no match for his strength.

As he kneaded my breasts, he panted that he couldn’t take it anymore. His fingers quickly found their way between my legs and expertly began to tease me. The unfamiliar yet intense pleasure made my breathing rapid, and the words I had wanted to keep saying no to gradually came out broken and halting.

“We can’t do this... this isn’t right...” I was still making my final struggle.

He nodded, but didn’t stop his hands. Instead, he bent down and sucked on my nipple, while his fingers continued to go in and out below, teasing me. Waves of pleasure surged up, and I couldn’t help making a sound. Just as I was almost about to sink into it, he suddenly pulled his fingers out and replaced them with his already hard, hot sex pressed to the entrance.

“Sis, I’m going in.”

Before I could fully refuse, he thrust forcefully, entering completely.

The initial swelling pain made my eyes well up, and I instinctively wanted to push him away. He paused for a moment, whispering, 'It won't hurt in a moment,' then began to slowly thrust. Gradually, the pain was replaced by an unfamiliar sense of fullness and pleasure. I bit my lip, but my body involuntarily began to match his rhythm.

“So tight… sis……” he panted, his movements gradually quickening.

Only the subtle sounds of flesh colliding and my uncontrollable moans remained in the room. I don't know how long it had been when intense pleasure accumulated to its peak, and I experienced an orgasm in a female body for the first time. My body trembled violently, inner walls contracting continuously. He didn't stop, continuing to thrust until he himself released inside me with a low roar.

Afterward he held me tightly, repeatedly apologizing, yet also asking whether we could continue in the future.

I looked at the ceiling, my mind in turmoil. Finally, I sighed and said, 'This matter absolutely must not be known by the family. Also, from now on, you are not allowed to cum inside without my permission.'

He immediately agreed, and even pushed his luck by calling me “wife.” I was both shy and angry, but in the end I still followed him and called out “husband.”

Since that day, the boundaries between us completely disappeared.

University life appeared calm on the surface. Every day, I took the bus to school with my second brother. Sometimes we would separate for classes on campus and meet up afterwards. On the surface, we were just ordinary siblings, but in reality, whenever we had a chance to be alone, our bodies would entangle.

Once in a secluded corner of the school library, he pulled me into a gap behind the bookshelves when no one was around. He rubbed my breasts over my clothes, his fingers probing under my skirt. I bit my lip to keep from making a sound, but eventually came in his hand. Another time was in a pavilion in the park near his house. Late at night, he hugged me from behind, lifted my skirt, and entered directly. The mix of tension and pleasure made that time especially intense.

At least twice a week, he would find an opportunity to have sex with me. Sometimes during the day when we were alone at home, sometimes late at night after everyone was asleep. The positions gradually became more skilled from the initial awkwardness. While juggling university coursework and clubs, I became immersed in this immoral yet inescapable relationship.

He became more and more clingy. When it was just the two of us on campus, he would hold hands with me, put an arm around my waist like a couple, and even kiss me or touch my body in secluded corners where there were few people. Whenever other men showed interest in me, he would become especially vigilant and do everything he could to interfere. I sometimes thought about ending the relationship and dating normally, but I simply could not do anything about him. As time went on, I seemed to have really become his exclusive possession.

In sophomore year, we started renting hotel rooms more frequently. Sometimes, right after class before it was even dark, we'd find a nearby daily-rental suite. Often, we wouldn't even bother fully undressing before eagerly tangling together. He liked entering from behind, one hand reaching around to fondle my breasts, the other hand stroking my fully feminized genitals back and forth. He often made my legs go weak, and I could only lie on the bed, taking it.

Once during exam week when the pressure was high, I originally wanted to refuse. But he came in while I was studying late at night, carried me from the desk to the bed. That time he was especially gentle, kissing my neck and collarbone, his movements slow and deep after entering. After finishing, he held me and whispered: 'Sis, I think I really can't be without you.'

I didn't answer, just buried my face in his chest.

After junior year, our relationship became more stable and also more secretive. The family seemed to vaguely sense something off about our closeness, but didn't expose it. After my sister got married and moved out, there were more rooms available at home, but we still preferred sleeping in the same one. On the surface, it was to take care of each other; in reality, it was for convenience at night.

Sometimes he pushes the door open while I'm showering and joins directly. Hot water washes over our entangled bodies, the steam filled with suppressed gasps. Afterward, I often lean against him, feeling his semen trickle down my thigh, feeling both ashamed and strangely satisfied.

During the summer vacation before university graduation, we did it almost every day. We'd go out together during the day, and at night we'd close the door at home. He learned more tricks, using his tongue to please me, and letting me ride on top of him. I gradually changed from being passive at first to becoming active. Sometimes I'd even pull him back for another round as he was about to leave.

After graduation, I found a job related to foreign languages, while he entered a company introduced by his family. Life superficially returned to an ordinary track, but whenever there was a chance, our bodies would honestly entangle together.

Some secrets, once started, can never be stopped.

And we, all clearly know this.

Another few years passed in the blink of an eye. I had completely adapted to my female identity and body, and my university studies, club activities, and part-time jobs all concluded smoothly. On the surface, I was an ordinary office worker, but privately, I maintained this relationship with my younger brother that was both sibling-like and lover-like.

Every time he enters my body, that feeling mixed with guilt and intense pleasure still makes me sink deeper each time. The memories accumulated over four years of university—the shelves behind the library, benches in campus corners, beds in daily rental suites, the bedroom at home in the middle of the night—all became indelible imprints.

One night, he suddenly asked me: 'If you could do it over, would you still drink that beverage?'

I was silent for a long time, finally giving a slight nod.

“At least... I met the you who exists now.”

He didn’t say anything, just held me even tighter.

The city lights outside the window are bright. University ended long ago, but our forbidden story continues.

The first year after graduation, life superficially returned to the most ordinary track.

I joined a medium-sized trading company as a foreign trade specialist, exchanging emails with overseas clients, organizing documents, and occasionally traveling for work. My younger brother got a job at a logistics company through a relative's referral, working in entry-level management. We still lived at home, each sleeping in our own rooms—at least on the surface. Whenever our parents fell asleep at night, he would gently push open my door.

Sometimes it's just hugging and kissing, sometimes we do it until just before dawn before parting. Our bodies are already familiar with each other, and there's almost no resistance when entering. He likes to hold me from behind, one hand covering my lower abdomen, the other kneading my breasts, thrusting slowly but deeply. I bury my face in the pillow, trying not to make too much noise. Afterward, he helps clean me up, kisses my forehead, and then silently returns to his own room.

Such days lasted for a long time.

Once after a company dinner, I had a bit to drink and was a bit unsteady on my feet going home. He happened to be waiting for me in the living room. My parents were already asleep. He helped me back to my room, and after closing the door, he didn't hold back. That night he was particularly forceful, pressing me against the desk, entering from behind with urgent, heavy movements. I braced my hands on the desk, my body leaning forward slightly with each thrust, only able to let out intermittent whimpers. After finishing, I could barely stand. He carried me to the shower, washing away the stickiness with hot water, then did it a second time in the bathroom.

Amidst the steam from the hot water, he hugged me from behind, his lips close to my ear asking, 'Still want to run away?'

I shook my head, leaning against him: 'There's no escaping.'

He said, “Then don’t run,” and then became hard again, filling me once more.

After work gradually stabilized, we began renting rooms outside more frequently. Sometimes we went right after work on Friday, sometimes on weekends using excuses like meeting friends. The beds in daily rental suites were larger than at home, and we also worried less about noise. He would let me ride on top of him, moving on my own, his hands gripping my waist and pressing down until I came first, then he would speed up to release. Sometimes he would use oral sex to make me climax first before entering. His skills were more proficient than in college, and he also knew better how to please me.

I gradually became more active.

Once he worked overtime very late, I cooked a midnight snack and waited for him. He came in exhausted, but I pulled him into the room, knelt down, and unzipped his pants. At first he tried to refuse, saying he was too tired, but when I took him into my mouth, he quickly hardened. I swirled my tongue around the tip, then took him all in, mimicking the rhythm he'd taught me before. He gasped, holding my head, and finally came in my mouth. I swallowed it all and looked up at him. His eyes darkened as he pulled me up, pressed me onto the bed, and entered me forcefully in return. That time he went at it fiercely and for a long time, only stopping when I begged for mercy.

The physical rapport deepens, yet the heart occasionally feels uneasy.

Once at the company, a male colleague expressed interest in me and asked me out to dinner after work. I originally wanted to refuse but was troubled by his persistence. When Er Di found out, he was unusually quiet that night. When he came into my room at night, without a word he flipped me over and entered from behind, his movements much rougher than usual. I was thrust forward, only able to grip the sheets. After finishing, he held me, his voice muffled, 'Don't get too close to others.'

I didn't argue, just nodded.

Since then, I became even more cautious about invitations from other men. It wasn’t because I was afraid, but because my body and habits had already been completely occupied by him. Occasionally, late at night when everything was quiet, I would wonder how long such a relationship could last? Parents would eventually grow old, my older sister would sometimes come home, and relatives would visit too. If the day comes when what is wrapped in paper can no longer be hidden, what should we do?

There are no answers to these questions, and no one to ask.

Another two years passed in the blink of an eye.

I got promoted and started leading a team. He also gradually gained more importance at the company. On the surface, we were ordinary siblings, commuting together, eating together, handling household chores together. Privately, our physical entanglement never stopped. Sometimes we did it for several consecutive days, sometimes we went a week apart due to busy work. But whenever there was an opportunity, desire would reignite.

One weekend, our parents went to visit relatives in the south, leaving just the two of us at home. For those three days, we barely wore proper clothes. We did it on the couch during the day, in my bed at night, and he even entered me from behind while holding me in the kitchen. After finishing, we were often too lazy to clean up, just sleeping while holding each other. The feeling of dried semen on my thighs became familiar, even somewhat addictive.

On the third night, he suddenly asked me, 'If one day we must part, what would you do?'

I was silent for a long time, finally saying: 'Then let's separate. But before that, I just want to continue.'

He said nothing else, only held me tighter and entered me again. That time was especially slow, and especially deep. Every thrust seemed to be confirming something. My legs were wrapped around his waist, my fingers digging into the muscles of his back, enduring everything he gave me.

When the climax arrived, I bit his shoulder, my body trembling violently. He also released inside me at the same moment, the scalding liquid pouring in, bringing me to the peak once again.

Afterward we lay side by side, listening to each other's heartbeats.

Occasionally, car headlights swept past outside the window.

The city is still running, life goes on. And the secret between us has become as natural as breathing, yet as inescapable as shackles.

After some time, my older sister suddenly came back with her child to stay for a few days. With more people in the house, we had to be even more careful. At night he could only sneak into my room, his movements so light there was almost no sound. Once, the child cried and fussed in the middle of the night, and my sister got up to comfort them; we almost got discovered. After that, we did not touch each other for a full week, yet the desire only grew more intense under the suppression.

The night after my sister left, he almost pinned me against the wall in the entryway as soon as he entered. My skirt was lifted, my panties pulled aside, and he entered directly from behind. I braced my hands against the wall, my body swaying back and forth with his thrusts. It had been too long, so there was some aching fullness upon entry, which quickly transformed into intense pleasure. He covered my mouth with one hand, while the other kneaded my breast, his movements urgent and rough. Before long, I came in his hand, my inner walls contracting violently. He panted heavily, speeding up, and finally released everything inside.

After it ended, we leaned against the wall panting. He hugged me from behind, his lips pressed against the side of my neck: 'Did you miss me?'

I nodded, my voice still a bit hoarse: "Want to."

He smiled and carried me back to the room, then did it a second time.

And so the days passed one by one.

Work, family, secret desires—the three intertwine to form our daily life. Occasionally, I look at my body in the mirror—the completely feminized curves, the faint marks he left, and the interspersed look of surrender in my eyes. I wonder, if I hadn't drunk that beverage back then, what would I be like now? But every time he enters me, these questions are completely thrown to the back of my mind.

One day he suddenly said he wanted to rent a small apartment outside, a place that belonged only to the two of us. I hesitated at first, but later agreed. Finding the place, signing the lease, adding simple furniture—the whole process felt like building a real relationship. The apartment wasn't big, but it was enough for two. From then on, we had more time where we could completely relax.

There, we no longer needed to suppress our voices. He would let me cry out, try more positions, and hold me to chat afterward. Sometimes we talked about work troubles, sometimes childhood memories, sometimes we didn't talk about anything, just stayed quietly together.

The physical compatibility had reached a point where no words were needed. He knew how to quickly arouse me, and I knew how to quickly make him hard. Sometimes, just a look would lead to kissing and undressing. After penetration, it was often me who came first, and then he would release. Sometimes he would deliberately hold back, making me climax twice in a row before stopping.

This kind of life has continued until now.

University was already a thing of the past, yet the taboo that began on campus only tightened its grip in the years of adulthood. We never discussed the future, nor did we discuss an end. Just day after day, entrusting our bodies and secrets to each other.

One night, on the bed in the suite, he held me from behind, moving in and out slowly. With my back to him, I felt the warmth of his chest and the fullness below. He suddenly lowered his head and whispered in my ear, 'Jiajuan, I love you.'

That was the first time he said the word 'love' so explicitly.

I didn't answer immediately, just clasped his hand in return, intertwining our fingers.

After a long time, I softly said, 'Me too.'

His movements paused slightly, then became deeper and more forceful. I buried my face in the pillow, enduring the sudden increase in the pounding. Pleasure piled up quickly, and before long I reached climax. He also released inside my contracting inner walls, and the scalding liquid filled me again.

Afterward he did not withdraw and just kept holding me in that connected position.

The city lights outside the window remain bright.

Our story continues. There is no ending, nor does it need one.

Just two adults, in the crack between kinship and desire, handing themselves completely over to each other.

And time was still moving forward.

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