At night, your girlfriend/sister sneaks into your room and have sex.

After your parents got home early by your dad's company calls him back to work and your shapeshifting girlfriend still stucks in your sister's appearance, your shapeshifting girlfriend/sister stays a little while longer until your parents will go out. But right now, you both enjoy your parents dinner with each other. After the family finishes the dinner, your transformed girlfriend-in-sister helps your mom washing the dishes and keep pretend to be your sister without getting caught. Later on that night, you go to your room and get ready for sleep, you slept in a pair of sweat pants and nothing else. Suddenly, you see your 'sister' came into your room late one night, and when you saw her body in her satin nightgown, you could see the outlines of her nipple. She wasn't wearing a bra. You couldn't hide your hard-on from her. "Ba... I mean 'sis'. What are you doing here?" you ask.

"Shhh~ quiet, bro. Our 'parents' are, like, sleeping." your sister/girlfriend says quietly.

"What if they wake up and come to check on us?" you ask again.

"Oh, you're like, worry too much. They're not, trust me, bro. Besides, that's a risk I am, like, willing to take to spend a night with you." she swooned and pressed her body even closer up to you. "Like, what you see?"

You look at her in response as her eyes were wide and honest, so as her lips quivered. You couldn't say no to this girl. You give her a slight nod as she embraced you. Her hands nervously reached down your body. Slowly her hand reached towards you crotch on your pants. With that, she start by pulling your pants and then your underwear down as she reveals your big dick, standing straight out. "Teehee, your cock is like, really big, bro. I didn't like, realize your 'girlfriend' like about you." your sister responds softly. "Now without further to do, like, shall we get started?"

After that, your 'sister' take off her nightgown and reveal her whole body is completely naked, not even a bra or panties on. "Teehee, I know you like, wanted to touch these huge knockers, bro." she says as she grabs both your wrists and placed your hands on her breasts. "Mmmm... yes... Touch them and squeeze them, bro. It felt so good."

Come to think of it, your girlfriend/your sister's breasts feels so good to touch them. Not only that she was your former girlfriend who shapeshifting into your own sister, but also her body was so amazing. It was barely a handful as you massage her chest, she let a soft moan escape before she restrained herself, trying to avoid making sound that could disturb your parents' sleep. "Now, bro. Why don't you put your cock inside my puss, so like, we could starts making love?" she quietly asks.

"Okay, 'sis'. Is that what you wanted..." you respond as you fumble a bit, rubbing your cock against her crotch, hoping to find the correct hole and angle because it's hard to see in the dark. Then, when you finally found it and slid it inside her.

"Mmmm,... oh...yeah... that's the stuff..." your 'sister' softly moans. "Try not to get loud, 'bro'. We like, don't want to disturb 'our' parents."

You nod as you thrust inside her softly and gently without make any noises on your bed. The couple laid sideways, face to face. Your cock soaking inside of her for a little while. Her pussy insides enveloped and gripped you. You entire being are focusing at her, and the sensations are absolutely stunning. Slowly, you both increased your pace. The intensity is growing. Your 'sister' leans her head back as she shuddered and shocks ran through her body. Her grip thightetens in pulses. Feeling her body and seeing her taken by passion as you cum inside her. For a short while, you both laid together and cuddle on your bed. "That is like, the best night sex I've, bro." your girlfriend/sister responds. "Let's say we like, continue for tomorrow, shall we?"

"Whatever you say, 'sis'." you replies as your 'sister' kisses you goodnight. And then, she stealthily and quietly walks out of your room and return to 'her' room without getting caught.