He waited in his room. His mother told him he could not have a regular girl, they were too fragile. He didn't understand, but she promised he would thank her if he would trust her and wait in his room. She was going to give him something that would make him believe.
After a few minutes, he heard the doorknob turn. The door opened slowly and his little sister stepped in, closing the door behind her. She walked over to his bed and jumped up next to him. She whispered into his ear, "Mommy told me to tell you a secret". She leaned away watching him waiting.
"Well, tell me ya little brat"
She laid on his chest looking directly into his face,"Mom says we are different because daddy was from far away. She says that because of the two of them had us, we are able to do things different, that we can't do things with other people or we would hurt them. She said we can't be hurt like them so we are...perfect mates. She said we will be stronger when we mate and that you should do whatever you like with me now.
She sat up and pulled her dress off. She had no panties. She next undid his belt and jeans. She looked at him and said "She said you would know what to do next"
He stared into her tiny pussy as she stood up. No way he could fit in her, but some instinct told him he had to fuck her right now. His cock tore through his underwear as it swelled. He pulled her down next to him and hurriedly stripped. He knelt on the bed grabbing her up by her arms. His grip was fierce and she squeaked as her arms bruised. He yearned for her and he pulled her against himself humping against her belly and flat chest. His cock felt warm and wet and so good. He felt a burning sensation and looked down. Her eyes were rolled back and she was gasping between his thrusts. He pushed her away and saw his dick covered in her blood sliding out of her torso. As he pulled out, her guts began to pop out and there was a squirt of what smelled like stomach bile. Now he knew, he had to continue to save her. He plunged back in pumping with urgency into her, churning her stomach contents as the acid burned his foreskinthe feeling of his testicles slapping her spilling guts drove him wild and he ejaculated into her stomach until she vomitted his sperm. She finished puking and she looked up at him and smiled. He raised her to his mouth and kissed her drawing in his semen and her bile. They were mated now, having survived their awakening. He would have many years of pleasure ripping her body and watching it heal before she could bear their children.