Human Behavior Observation Experiment
Copyright© 2025 by danbaifen
Chapter 20
Incest Sex Story: Chapter 20 - That night, Allison had a nightmare. She dreamed that she had committed incest with her son and got pregnant and married, and people found out. Everyone called her a slut, a shameless bitch, and a beast... She screamed "No..." When she woke up, she was already in tears.
Caution: This Incest Sex Story contains strong sexual content, including Incest Mother Sister
Ella finally nodded, tears bursting down her cheeks.
She threw herself into her brother’s arms, bursting into tears.
“Brother ... I’m sorry ... I shouldn’t have said that to mom ... I just couldn’t accept it for the moment ... I actually love this family the most...”
Colin stroked his sister’s hair with relief and kissed her forehead.
“Ella, I’ve known for a long time that you have a kind and soft heart. Go talk to mom. She needs your understanding and support the most right now.”
Ella burst into laughter and looked at her brother with gratitude.
She wiped away her tears and made up her mind to reconcile with her mother.
At this moment, Allison was grieving in her bedroom, not knowing how to face her daughter’s resentment.
Suddenly, there was a knock on the door and Allison hurriedly tidied her appearance.
When she opened the door and saw her daughter standing there, she was stunned.
Ella looked at her mother with tears in her eyes and a guilty look on her face. She bit her lip, hesitated for a long time, and finally said: “Mom ... I’m sorry ... I shouldn’t have treated you like that...”
Allison was overjoyed and burst into tears.
She pulled her daughter into her arms and held her tightly.
“Ella ... I am sorry for you ... I am an incompetent mother...”
“Stop it, Mom.”
Ella choked up and hugged her mother back.
“I understand ... You and brother really love each other ... I will support you...”
The mother and daughter hugged each other and cried, and finally reconciled their past grudges.
This situation made Colin feel mixed emotions.
He smiled with relief and sighed inwardly: Sure enough, love can resolve all conflicts.
From now on, his mother is his wife, his sister is his lover, and their family will live happily together.
Allison and her daughter reconciled, and she had both love and hate for her son’s brainwashing of his sister. However, she knew that for the sake of the overall situation, she could only accept this result. Now this family has been controlled by Colin.
She had a vague premonition that her daughter would be captured by her son sooner or later and become his exclusive lover.
Allison felt guilty and excited at the thought of mother and daughter serving the same husband. She knew that she had fallen beyond redemption...
Since daughter Ella accepted the relationship between mother and son, the atmosphere in the family has become subtle.
Allison is both Ella’s mother and her nominal sister-in-law; Colin is both Ella’s brother and her stepfather.
For a moment, the three of them felt a little uncomfortable getting along with each other.
Colin was very calm about it. He ate and drank as usual and was affectionate with his mother without hiding anything from Ella.
Sometimes when Ella saw the mother and son kissing, her face would unconsciously turn red and her eyes would flicker with embarrassment, but she would no longer resist angrily like before.
Allison secretly observed her daughter’s reaction, feeling mixed emotions.
On the one hand, she was sincerely relieved that her daughter finally understood her; but on the other hand, she was secretly worried about her daughter - when her son brainwashed her with just a few words, could her daughter still stick to her bottom line? She was afraid that her daughter would follow in her footsteps, fall into her son’s love, and become his forbidden delicacy...
“Mom, what are you thinking about? Why do you look so serious?”
Colin walked behind her at some point, suddenly put his arms around her waist, rested his chin on her shoulder, and spoke in a teasing tone.
“nothing...”
Allison came back to her senses, feeling a little guilty, and quickly changed the subject.
“What do you want for dinner? Do you want mom to cook you some of her signature dishes?”
Colin chuckled and reached his hand restlessly into his mother’s clothes, stroking her bulging belly.
“You, since you are pregnant, please don’t go into the kitchen. If you need anything, just tell Ella. She is our sweetheart now.”
Allison could tell there was something behind her son’s words and subconsciously glanced at her daughter who was not far away.
Ella was busy scrolling through her phone, ignoring the affectionate behavior between her mother and brother.
Ever since she found out her mother was pregnant with her brother’s child, she became more considerate to her mother and took on almost all the housework.
Allison should have been pleased with her daughter’s understanding, but she felt vaguely uneasy.
“Mom, can you give me a daughter?”
Colin’s hands dishonestly rubbed his mother’s breasts through her clothes and breathed erotically into her ears.
“By then, we will be a family of four, living happily together...”
Allison blushed, gently pushed her son away, and whispered: “Bad boy, what nonsense are you talking about ... Besides, whether the child is a boy or a girl, the mother can’t decide...”
Colin shrugged indifferently and kissed his mother in front of his sister.
“Both sexes are good, the more the better. Sister, don’t you agree?”
Ella raised her head when she heard that, her cheeks flushed, and she looked at them with complicated eyes.
She hesitated to speak, and finally just smiled and said nothing.
Allison’s heart skipped a beat, and she had a feeling that her daughter had begun to have feelings about this “stepfather and stepmother” relationship.
Colin seemed to see through his mother’s thoughts. He blinked at her with a meaningful smile on his face.
Allison felt that things were heading out of control.
The son was eyeing his daughter covetously, and the daughter seemed to have begun to have secret fantasies about this abnormal relationship.
She had a vague feeling that it might not be long before she and her daughter would become her son’s playthings...
Thinking of the erotic scene of mother and daughter serving the same husband, Allison felt guilty and secretly excited...
“Sister, please say something. Do you want your sister-in-law to give you a nephew or a niece?”
Allison slapped her son and blushed as she said, “Hate it, what sister-in-law ... nonsense!”
Colin said seriously, “Why are you talking nonsense? Isn’t my brother’s wife my sister-in-law? Sister, don’t you think so?”
Ella also blushed and didn’t know what to say. She nodded and shook her head.
“Be good, sister, call me sister-in-law!”
Colin pointed at his mother beside him and looked at Ella.
Allison’s body trembled involuntarily, and her face turned red with embarrassment.
She glanced at her daughter’s reaction, fearing that she would not be able to accept this title.
Unexpectedly, although Ella blushed, she did not show any resistance. She blinked her big watery eyes, as if she was playing a prank, and called out sweetly: “Sister-in-law~”
“ah?”
Allison didn’t know how to react for a moment and looked to her son Colin for help.
Colin, with a wicked smile on his face, hugged his mother’s waist, winked at Ella and said, “Did you hear that? Your sister-in-law is embarrassed by your calling her that. Ella, be good, call her that from now on, after all, mom is your legitimate sister-in-law.”
Allison felt both sweet and terrified.
She felt extremely excited when her son hugged her so intimately in front of her daughter.
But she felt uneasy when Ella called her sister-in-law so obediently.
She was afraid that this abnormal relationship would affect her daughter’s mind.
However, at this point, Allison has no choice. In order to retain her son’s love and for the sake of the baby in her belly, she can only continue to acquiesce to all this happening.
So, Allison blushed and whispered to her daughter: “Ella, be good...”
It was as if she had accepted her new identity as sister-in-law.
Colin was secretly delighted when he saw this, as his plan was being realized step by step.
Soon, his sister will willingly lie under him and become another of his forbidden love ... Thinking of his sister’s young body, Colin can’t suppress the desire in his heart.
Allison’s heart skipped a beat when she saw the desire burning in her son’s eyes.
She knew that her daughter had completely fallen into her son’s control.
And I can only go with the flow and sink with my daughter...
As expected, Allison soon stumbled upon her son and daughter kissing each other.
She knew in her heart that her son had been plotting against her daughter for a long time, but he had restrained himself because of her presence.
Now that I’m pregnant, I can’t let him do whatever he wants like before. My son has a strong sexual desire, and he feels uncomfortable with it, so naturally he turns his attention to my daughter, who is 70% similar to me.
Allison sighed and left the scene sadly.
Colin hurriedly caught up, hugged his mother from behind, and whispered in her ear: “Mom, don’t think too much. The person I love most will always be you, but you are pregnant now, so it is not convenient for us to be intimate. I really feel uncomfortable ... Can you understand me?”
Allison closed her eyes in despair and murmured: “I know everything ... but she is your biological sister ... it is wrong to do this...”
Colin kissed his mother’s cheek, his tone gentle but unquestionable: “Mom, have you forgotten? We are husband and wife now. As for Ella, even if she is your sister-in-law and my stepdaughter, there is nothing wrong with that. Besides, we have already crossed the bottom line of human relations, what else is there to worry about?”
Allison knew her son was right, but she couldn’t completely let it go.
But, what can she do?
She has fallen beyond redemption.
Just then, her daughter came and found her.
She bit her lip, hesitating to speak, and seemed to have something to say that was difficult to say.
Allison hugged her daughter and asked with concern: “Ella, if you have anything, just tell mom ... and sister-in-law.”
Seeing her mother calling her sister-in-law, a hint of surprise flashed across Ella’s face, but then it dimmed again.
She stammered, “Sister-in-law ... Sister-in-law, actually ... since I accepted your relationship with my brother, my worldview has become very strange ... I always feel that incest, although immoral, is full of ... excitement...”
Allison’s heart sank, and the ominous feeling grew stronger.
Ella blushed and mustered up the courage to say: “Sister-in-law, I ... I also want to join you ... to be my brother’s woman...”
Although Allison was mentally prepared, she was still stunned and speechless for a moment.
She didn’t expect that her daughter would fall so quickly, it was completely beyond her expectations.
If the upper beam is crooked, the lower beams will be crooked too. If you have an affair with your son and your daughter follows suit, who can you blame?
At this moment, Colin stood at the door without knowing when, with a confident smile on his face, it seemed that everything was under his control.
Allison felt dizzy, it all happened so suddenly.
Her daughter’s depravity and her son’s scheming caught her off guard.
She sat down dejectedly on the edge of the bed, looking at the brother and sister in front of her, not knowing what to say.
Perhaps from the beginning, she shouldn’t have allowed this abnormal relationship to develop to an irreversible point...
But now, it’s too late.
Allison had a vague feeling that she and her daughter would become the mother and daughter of her son, and there would be no turning back...
“Mom ... sister-in-law ... I have discussed it with my brother. As long as you can accept it, I am willing to be your mistress...”
Ella looked at her mother timidly and mustered up the courage to say these words.
Allison looked at the brother and sister in front of her, feeling mixed emotions.
She didn’t expect things to develop to this point.
Daughter Ella not only accepted the incestuous relationship between her and her son, but also asked to join them and become Colin’s concubine.
Colin was eloquent and tried his best to comfort his mother and said sweet words to her.
“Mom, don’t worry, I will always love you the most. At best, your sister is my tool for sexual gratification when you are not convenient. No matter her status, she is not as good as you, my first wife.”
Colin put his arm around his mother’s shoulders and whispered affectionately in her ear.
Allison blushed and felt a little shaken.
She knew very well that her son had been feeling uncomfortable ever since she became pregnant.
She couldn’t bear to see him in so much pain, but was also worried that he would really go out and find a woman.
Instead of that, it would be better for him and Ella...
Thinking of this, Allison sighed and nodded slightly.
Colin was overjoyed to see his mother agree.
He took his sister’s hand and brought her to his mother.
“Ella, from now on mom is your big sister, you have to listen to her and respect her, understand?”
Ella glanced at Lu Qingyun, her eyes full of admiration.
“I understand, big sister. I will definitely take good care of my brother and won’t let you worry.”
“Good boy, baby”
Allison touched her daughter’s head, her tone gentle and helpless.
“Mom doesn’t want you to go astray, but since you’ve made up your mind ... Mom won’t stop you. But you have to remember, we are both your brother’s women from now on, so you have to respect him. When he’s around, don’t call me mom, call me sister-in-law or elder sister.”
“Um!”
Ella nodded obediently and smiled sweetly.
“Don’t worry, big sister. I will definitely serve you comfortably. We sisters work together and will definitely make you feel like you are in heaven!”
Allison shook her head helplessly, feeling mixed emotions.
She never thought that one day she and her daughter would share a husband. And this man was actually her own son! She knew it was ridiculous, but she had to accept the reality.
Allison silently accepted the fact that her daughter became her son’s concubine.
In order to keep her son’s heart, she had no choice.
But when she saw Ella’s innocent smile, her heart ached again.
Oh my God, what kind of road of no return did she lead her daughter to?
Allison closed her eyes in despair and let her son hold her in his arms...
Ella became her brother’s concubine as she wished. She knew that this was due to her mother’s sacrifice and magnanimity. She also knew the importance of her mother in her brother’s heart, so she was more filial and obedient to her mother than before, and her care for her mother could be said to be meticulous.
Allison felt complicated as her daughter became more and more attentive to her.
“Sister-in-law, I’ve cut the fruit for you. Eat more.”
“Sister, I made some pork rib soup, which is especially good for pregnant women. I’ll serve you a bowl.”
Ella always referred to her as “sister-in-law” and “elder sister”, and she took good care of her mother.
Her filial piety was no less than before, making her mother feel respected like never before.
Gradually, Allison’s guilt faded. She thought, since both children were so sensible, what was wrong with incest? Besides, Colin promised her that no matter how many women he had, she would always be the only one he loved. With this guarantee, Lu Qingyun thought it was good to let her daughter share the obligation of serving her son.
So, Allison began to do her best to be a pregnant woman with a safe pregnancy and left all the housework to Ella.
She enjoyed the love of her son and daughter with peace of mind and no longer felt bad about the incest.
Colin was delighted to see his mother gradually accepting this abnormal relationship.
He became even more unscrupulous in his flirting with his sister and was intimate with her in front of their mother.
Allison just smiled gently, as if she was condoning her child’s mischief.
“Big wife, my little wife and I are going to make an adult tonight for fun, so please don’t peek~”
Colin teased.
Allison blushed and pretended to be angry: “Oh, you two ... you are so grown up and still so childish!”
But the smile on his lips couldn’t be concealed.
Seeing the happy look on his mother’s face, Colin knew that she really accepted it.
He hugged his mother, gently stroked her bulging belly, and said expectantly: “Mom, when this child is born, our family will be happy. I will be the father, you will be the mother, and my sister will be the aunt ... I can’t wait!”
Allison leaned in her son’s arms and blushed when she heard this.
She spat softly, “You’re the only one who’s thinking about it!”
Ella, who was standing by, was also extremely shy after hearing this, and said angrily: “Brother, how can you talk about this in front of your sister-in-law ... It’s so embarrassing!”
Allison looked at the flirting brother and sister in front of her with satisfaction, and a warm feeling surged in her heart.
She sighed, “You two have such a good relationship. Just get along well with each other and don’t let your mother worry.”
“How can that be possible, sister!”
Ella blinked her eyes and smiled sweetly, “No matter how good my relationship with my brother is, it’s not as deep as the relationship between my brother and his sister-in-law! As a younger sister, I have good sense and will never fight with my sister-in-law when it’s time to give in!”
Allison blushed at her daughter’s words, but was also very happy.
She knew that her daughter truly regarded her as her sister-in-law and would never threaten her position in Colin’s heart.
Perhaps, this kind of family composition is the most harmonious?
Colin kissed his mother’s lips at the right moment, then turned around and hugged his sister, announcing, “Come on, little wife, let’s go back to the room and make babies, leaving the big wife here alone to cool off!”
Ella stuck out her tongue and let her brother pull her into the bedroom.
At the end, he turned around and reminded her: “Big sister, have a good rest! If you need anything, tell me!”
Allison watched her son and daughter go back to their room affectionately, and she didn’t feel awkward at all.
She touched her belly with a faint smile on her lips.
Perhaps, it is not difficult to accept incest, but it is difficult to let go of the shackles of the world.
Now that she has done it, she lives an exceptionally comfortable life.
Allison marveled at the wonder of fate.
She originally thought that incest would tear the family apart. Unexpectedly, the addition of her daughter brought her and her son closer. The family atmosphere is now more harmonious and happy than ever before. Perhaps, breaking the taboo of human relations may not be a bad thing? She decided not to worry about it anymore and enjoy everything she has now with all her heart.
After Colin and Ella had been loving each other like a young couple for about a month, one night they walked up to their mother hand in hand and proposed to have a group sex with her.
Allison couldn’t help blushing when she heard her son and daughter’s idea.
Although she had gradually accepted the incest with her son and even acquiesced in her daughter becoming her son’s concubine, this was the first time that three people had sexual relations at the same time.
Allison hesitated. She looked at her children who were full of expectation and said shyly, “You two always have some weird ideas. Can I, as a mother, really bear it while I’m pregnant?”
Ella quickly comforted her, “Don’t worry, sister! You are five months pregnant now, the fetus is stable, and there is no problem with having sex. Besides, my brother and I are here, we will be very careful. Don’t be restrained, just enjoy it!”
Colin also echoed: “Yes, mom, you see, Ella and I have been having fun for so long, and you are just standing outside watching us. How pitiful! We are a family, we should be together, and no one should be left behind!”
Allison was coaxed and deceived by the two, and finally nodded with a red face.
Seeing their mother’s shy look, Colin and Ella smiled at each other, both of them couldn’t wait.
At first, Allison was still a little hesitant.
But when her son’s cock broke into her wet vagina again and her daughter’s soft tongue set fire all over her body, she finally threw away her shame and began to scream.
“Ah ... son ... be gentle ... Mom is pregnant...”
“Big sister, your breasts are so soft ... After the baby is born, can I have a taste of your breasts?”
“Oh Ella ... you kid ... ah ... how can you be so...”
The three of them were breathing heavily and their bodies were colliding, and they soon fell into a crazy sea of desire.
The mother’s plump and soft body rolled between her son and daughter, sucking her son’s penis and entwining her lips and tongue with her daughter. This kind of immoral stimulation made Allison unable to stop.
“Son ... Mommy wants to give you a daughter ... Let her grow up to be your woman ... Yeah ... Then our family ... can be together legitimately...”
“Okay ... Mom ... I’m going to fuck you to death ... and make you give birth to a bunch of daughters...”
“Brother ... when the time comes, don’t forget me, your concubine ... wuwu...”
Colin and Ella stimulated Allison with each other and soon brought her to a climax.
Allison hugged her children tightly, her snow-white body twitching violently, enduring the wash of her soul. At that moment, she felt that incest was the most wonderful thing in the world.
Afterwards, the three of them lay in each other’s arms, enjoying the afterglow of the climax.
Allison gently stroked her son and daughter’s faces and whispered softly: “From now on, Mom’s body and soul will be completely handed over to you. You must love Mom well!”
“Of course! Big sister will be our woman from now on, we will spoil you to the sky!”
“Don’t worry, mom. No matter how many other women I have in the future, you will always be the one I love the most.”
Listening to her children’s sweet words, Allison closed her eyes happily.
She felt like a pregnant bitch, being loved by two masters in turn.
The days ahead will surely be even more lewd and exciting!
Allison completely threw away the constraints of ethics and morals and was determined to give birth to an incestuous child for her son.
And her daughter Ella was willing to be a concubine and form this deformed family with her and her son.
The three of them will embark on a more crazy and chaotic road of no return...
This home seems to never be at peace, and now there are new changes.
That day, when Colin went out to work, Ella suddenly found her mother.
She hesitated, her face flushed, as if she had something difficult to say.
“Mom ... No, big sister, I have been hiding something from you...”
Ella spoke carefully.
Allison patted her daughter’s hand soothingly and said softly, “Ella, Mom knows a lot has happened recently. But no matter what, you are Mom’s good daughter. If you have anything on your mind, just say it directly, don’t keep it in your heart.”
Ella bit her lip and mustered up the courage to say, “Sister, I ... I am like my brother ... I think you are beautiful ... I have fallen in love with you!”
Allison’s eyes widened in shock and she was speechless for a moment.
Seeing this, Ella quickly explained: “I know this is wrong ... but I really can’t help but be attracted to you. My brother can have you, so why can’t I? Mom, you can’t be partial!”
Allison was devastated. She never expected her daughter to have such feelings for her.
She stammered, “Ella, this ... how can this be possible? Mom belongs to my brother alone ... you, you can’t...”
Ella interrupted her mother and put her arms around her waist, making it impossible for her mother to resist.
“Why not? My brother can have sex with you, so why can’t I? I am willing to be my brother’s concubine, so you have to be fair to me, mom!”
As soon as she finished speaking, Ella kissed her mother on the lips.
Although it was common for the three of them to sleep in the same bed, the mother and daughter had seen each other’s most embarrassing and shameful appearances in bed, and they were accustomed to the sons kissing each other, but that was only done when Colin was present.
Now that her daughter suddenly confessed her love to her, and behind Colin’s back, Allison panicked and tried to push her away. However, her daughter was unexpectedly strong, holding her tightly and her tongue going straight in.
Just then, the door opened with a bang.
Colin came home early from get off work and happened to see his mother and sister kissing!
Colin stood there in a daze, staring at his mother and sister kissing passionately.
Seeing her son coming in, Allison hurriedly pushed her daughter away, lowered her head in shame, and wished she could find a crack in the ground to crawl into.
Facing her son’s shocked gaze, Allison felt ashamed.
She never expected that her well-behaved daughter would suddenly attack her, and her son caught her in the act! She was at a loss as to how to explain it all...
At this moment, she was in great torment.
Incest was absurd enough in itself, but I didn’t expect that even my daughter would have evil thoughts about me now.
As a mother, she couldn’t refuse her daughter, but she also felt sorry for her son ... Is this the consequence of ethical breakdown? What should she do?!
Allison stammered as she explained to Colin: “Dad, listen to me ... Ella and I were just confused for a moment, we are not that kind of relationship, don’t misunderstand...”
Colin interrupted his mother coldly, with a playful smile on his face: “Mom, since you’ve already started, don’t back off. It’s no big deal for a mother to have incest with her son and be intimate with her daughter. After all, we’re a family, so what’s the point of talking about ethics and morals?”
Allison lowered her head in shame, feeling extremely guilty.
Ella looked aggrieved, and threw herself into Colin’s arms and said coquettishly: “Brother, I’ve fallen in love with my sister-in-law, please don’t blame her, okay? I will still love you the most...”
Colin patted his sister’s head lovingly and said with a smile: “Silly wife, how could I blame you and mom? I wish you had a good relationship! Just remember, no matter how intimate you are, you are my woman and my Colin’s private property. Without my permission, you are not allowed to be intimate without permission, understand?”
“Of course...”
Allison blushed and nodded, feeling touched and ashamed by her son’s generosity.
Unexpectedly, her son not only did not object to her relationship with her daughter, but also generously “allowed” them to be intimate, on the condition that they both submitted to him.
Ella also hurriedly agreed: “Don’t worry, brother, we sisters will definitely ask for your consent when we get intimate next time. No matter what, we will always be your women, you are our sky!”
Looking at the incestuous brother and sister in front of her, Allison had mixed feelings.
She originally thought that breaking ethical taboos was an unforgivable sin.
But she didn’t expect that her daughter would also have evil intentions towards her, and her son not only tolerated them, but also wanted to keep them under control...
Have they, mother and daughter, completely become their son’s playthings?
Colin proudly admired the sight of his mother and sister bowing to him, and a twisted sense of pleasure welled up in his heart.
He understood that his tyranny had completely enveloped the family, and his mother and sister could not escape his grasp...
After everything was explained, the three of them couldn’t wait to take off their clothes after dinner and began to enjoy the forbidden pleasure.
The three people were naked, entangled in a ball on the bed, venting their almost crazy desires unscrupulously.
Colin eagerly took turns taking possession of his mother and sister’s bodies. His thick cock went in and out of the two women’s wet pussies, enjoying the ultimate service from the mother and daughter.
“Ah ... son ... be gentle ... you’re going to break Mommy...”
Allison panted softly, her plump, mature body rolling under her son, her snow-white breasts covered with lewd kiss marks.