Dipper sat on his bed, watching his sister sleep from the other side of the room, observing her, he had been watching her sleep for over a week now, fantasizing about everything he wanted to do to her; another fantasy popped into his head, and he let it play out for a while before turning his head away from his sister in shame. Dipper had constantly fantasized about his sister, but still didn't know what it looked like. At that moment an idea popped into his head, his sister was a relatively heavy sleeper, and slept with just a large t-shirt over her underwear. Dipper quietly tip-toed over to his sister's bed, she lay on her back with her right arm laying over her chest, her left leg bent slightly to where the foot touched the other; it looked like she had kicked her covers off in her sleep. Mabel's breathing was steady, and the young boy watched on in awe as her chest rose and fell with every breath. Dipper took a deep breath himself, and carefully lifted his sister's shirt to reveal her panties; they were light pink with a cat in the middle. With trembling hands, Dipper grabbed the elastic band and gently pulled them down. Our young perve- ….Dipper gasped at the sight before him, his mind was racing as it came up with fantasy after fantasy, his thoughts were quickly interrupted by the sound of his sister waking. "What the….hey!" Mabel pushed her brother to the ground and angrily pulled her underwear up, "Y-you were looking at my lady parts when I was sleeping!" Dipper tried to think of an excuse to save him, but producing only stutters instead. "I-I-I was curious and just wanted to see." His face was red now as he stared at the wooden floor. Mabel's expression softened a little when she saw his embarrassment from being caught. "Aww, it's okay, I was curious too, up until those gnomes tried to capture me and make me their princess that is." Dipper smiled weakly, remembering that exact adventure. Out of the blue, she grabbed the waistband of his shorts, "Now, let's see what we have here." Mabel forcibly pulled off her brother's shorts and threw them aside, "it's just how I imagined!" Dipper couldn't stifle his erection from his sister's sudden fascination, and soon, his erect penis was right in his sister's face, now it was her face that was red, she looked at for a bit before grabbing it and sticking the head in her mouth.

She didn't do it because she knew how to, she did it because it felt like the thing to do, moving Dipper's penis further into her mouth she began to suck, almost like an instinct, she wasn't great at it, but she tried, and dipper didn't seem to mind. Dipper was moaning as his sister was giving him a blowjob, using her tongue, almost, in sync with her mouth, if she kept this up than our young Dipper might explode. To prevent this, Dipper stopped her, Mabel looked up with a look of confusion, maybe she wasn't doing it right, or maybe she was doing it too well. The siblings locked eyes before Mabel drew her brother into a deep kiss, and he kissed back, despite what had just been in her mouth. After she broke the kiss, Mabel lay on her back and lifted her shirt, exposing her underwear, Dipper didn't need to be told what to do, and he removed them and got to work. Dipper moved his tongue along her lips, making Mabel shudder at the sudden pleasure. "That feels sooo good!" Mabel blurted out, quite loudly.

"You have to be quite or you'll wake Gruncle Stan."

"Yeah, I suppose that's a bad idea, anyway don't stop!"

Before young dipper could voice his opinion, his head was shoved back into Mabel's crotch; she then crossed her arms and closed her eyes with a smile, happy that she had won. Dipper got back to work, licking her lips before slowly inserting a finger. He began to move his finger back and forth, while licking at the same time, soon after the first, he inserted a second finger. Mabel had spent the entire time just letting her brother do the work, while it felt good, she wanted something else.

Mabel stopped her brother and drew him into a long kiss, exploring his mouth as he did hers, after they broke the kiss; Mabel grabbed her brother's hand and led him to her bed. Once they were under the covers, Dipper slowly inserted his penis, careful not to cause too much pain to his sister; nonetheless, she seemed to be enjoying herself. He began to thrust, slow but deep thrusts, his moans were accompanied by those of his sister. Since it was the first time for both of them, they came quickly. They lay there, sweating and happy, holding each other tightly. This was soon interrupted by someone shifting their weight at the door, both Mabel and Dipper's head shot up at Wendy, who was standing in the doorway, with wide-eyes and frozen in place. Without saying a word she quickly turned around and walked away.

"Thinks she's going to tell anyone?"
"Nah."