He thought he was careful. No one would know he was climbing onto his sister when the clan was asleep, especially when they were passed out drunk after the feasts. There parents were dead from raiders and he made sure none of the clan used her. But the sight of her nude form sleeping near him every night was too much to resist. And when she welcomed his lust with eagerness, they were inseparable from then on. She wanted his protection and he wanted to fuck. She was merely a convenience. Very satisfying but to him, she was a toy for his pleasure.
After some months, her breasts grew and her belly bulged. He took little notice until he felt a kick as he lay exhausted on her.
If the clan found out he had sired a child with her, he would be cast out and she would be passed around the clan at the next feast to be fucked to death and then eaten.
They were doomed. Unless...
If she were gone he would be safe. He could also choose another girl from the clan since he no longer would have kin.
He would rather have kept her, but she would give them away soon enough. This way only one of them had to die...and he could enjoy it.
Next day they conspired to meet in the forest for some daylight humping. He took off to hunt and she went to gather herbs. They agreed to join at the old barn sveral miles in. No one goes there because it was rumored to be haunted. As soon as she arrived he was ready. He grabbed her as she laughed and tore off her clothing. "Hey I gotta wear that back home" she whined. She saw his fist cock back and felt the pain explode as the lights went out.
She woke with a headache and on her knees tied to a post. She winced as her eye ached where he hit her. Then she saw him walking toward her, nude and penis swelling as he grinned at her.
He knelt in front of her.
"Why did you hurt me and what are you doing tying me up?"
He placed his hand on her belly, "Do you know what is in here?"
She smiled, her eyes bright with joy, "It's your baby"
"It's a death sentence. They will rip you apart with their cocks and feast on your flesh and I will be cast out to starve or worse."
"We can run away together" she pleaded.
"Until we starve or are killed by the other clans. They don't take outsiders except to fuck or eat and kill."
He pulled out his knife from the dirt behind her, placing the sharp edge under her sternum. He sliced deep into her chest beneath her ribcage as he spoke, "This way, you will die quick and giving me pleasure and I won't have to be shunned. You will be remembered as the beautiful virgin that all the men wanted to open"
She gasped as he slit open her chest. Another slit down to open it wide enough and he reached inside. She groaned and gagged as he groped for the pulsing muscle in her chest. He hooked his fingers around it and pulled without squeezing. Blood ran from her wound and the sound of seperating tissue was drowned by her squeals. He looked at the beating heart still attached to her, pumping life through her. She stared at it in his hand, panting heavily. His cock was hard and oozing and he needed to fuck her one last time. The came a thought, he placed the knife at the tip of the heart slicing it open. Large spurts of blood pumped out. He crouched in front of her and she instinctively opened her mouth for him to enter. But instead he shoved her heart with its new cuntlike slit over his cock. He pounded into it, holding her against him, mashing against her fertile belly. The beating drove him wild as it tensed on his dick. When he came inside it, his sperm was pumped throughout her body and the pulses felt so good he stayed hard in her and came again. He waited for her to die, hoping he would climax again. He ripped open her belly and tore out her womb, cut her heart loose. He wanted to take her breasts too but they needed to stay for the wolves. He made a small fire, cooked her heart and child and ate them to conceal his crime. Then he gathered her torn garment, wrapped her with them and carried her body to the wolf den, leaving it nearby. He draped her over a log and spread her legs wide to entice the wolves to tear into her tender pussy to hide her loss of virginity.

He watched from a hilltop as they took the bait and made her little more than scraps and bones. She was discovered 3 days later when clan hunters found her scattered remains.