Katara whimpered, biting her bottom lip as she felt a shivering sensation go through her body. It was not the cold, she knew. The feeling of her brother's breath against her neck was enough to make her feel like she was burning up.
She blushed in spite of herself. She felt far less ashamed of the reaction her brother was eliciting from her than was probably proper, but the hot itch in her nether regions was rather distracting, and all she could think about was the sound of her brother's voice as he begged her to accept him, and the feeling of his body against hers as he embraced her.
She was of age, she knew. She had been giving her monthly sacrifice to Tui for a year and half, already, since shortly after the men of the tribe left to go fight in the war, in fact. According to the old traditions, as they had been taught to her by Gran-Gran, that meant she was a woman. The only woman near her brother's age in all the South Pole. Every other girl was either too young, or too old, to be marriageable, and Sokka was fast nearing the age where he would be expected to take a bride, especially given the circumstances.
The Southern Water Tribe had dwindled much from what it had been like when their grandmother was a young woman. Their numbers had been thinned by the near constant raids. Even counting the men who had gone off to war, their population was scarcely more than fifty, at the most optimistic count. Practically speaking, though, it was more like a couple dozen. Most of that was children and old wives, and a few wizened elders.
Out of all the tribe, Sokka was the only hunter remaining, the only fisherman, the only warrior. It would be a few years yet before even the oldest of the children would be old enough to help hunt or fish. Sokka was the chief provider of the tribe. Even with Gran-Gran and the mothers and children helping out where they could, casting nets and cleaning kills and laying stores, Sokka still had to do the work of several men, sometimes going out on the ice alone to hunt for several days in a row before returning with a slain tiger-seal in tow.
It was hard work even for a full hunting party of seasoned men, but Sokka rose to the task as best he could. Katara did what she could to help him, but even as much as she chastened him for his occasional sexist remarks, she knew she could not do his work. He had been trained and practiced in the way of the hunt since he was old enough to hold a club, and while as a waterbender she had the potential to far outstrip him in fighting and killing, it was for now only that: potential. At her current level of skill, she would only be a liability to him on the hunt. Her bending was not yet powerful enough to be of much use against anything larger than a snow shrew, and did not have any kind of skill with weapons.
Sokka was the only man in the South Pole, and Katara was the only woman anywhere near his age. Despite all that Gran-Gran had taught her about the old stories of the spirits of the ice and the wind and the moon and sea, the woman had also impressed upon her granddaughter the lessons of pragmatism.
In a year or two Katara would be old enough to take a husband and start raising a family. She knew this. She also knew that, to ensure the continued survival of the Southern Water Tribe, she would be expected to bear many children. Though non-benders could give birth to benders and vice versa, a bender parent was more likely than not to have bender children. Waterbending was an important part of their culture and heritage, as well as a powerful tool for the continued survival of the tribe. It was her implicit, unspoken duty to the tribe, as a woman and a waterbender, to do whatever it took to beget and raise waterbender children.
As her brother gently, pleadingly stroked her back, Katara continued to think, even in spite of the growing sense of longing in her own body for union with the man who held her. She thought, and she reasoned.
Her and Sokka's parents, Hakoda and Kya, both non-benders, had given birth to her, a waterbender, and Sokka, a non-bender. How? According to what little Gran-Gran had been able to teach her on the matter, bending was partly a matter of blood. It was a talent that tended to run in families -- in her own case, according to Gran-Gran, she had most likely inherited the talent from her mother's side of the family, for Kya, while a non-bender, had come from a family with a long history of producing waterbenders, and even if she had never manifested the ability it was clear that it had lain dormant in her blood nonetheless, seeing how it had manifested in her daughter.
Katara had inherited waterbending from her mother, who had carried the potential but never realized it. Yet Sokka was also a child of Kya. Her and Hakoda's blood ran through his veins, just as it did through Katara's. Even if the boy did not have the gift himself (and a very small part of Katara wondered whether he might not in truth have some manner waterbending potential), he still had the blood of his mother in his veins. It was still entirely possible that he could father waterbender children.
And if both she and her brother had the potential to pass on waterbending to any children they might have, than would it not be most efficient for them to join with one another, rather than someone with less potential in their blood? If pairing with her brother even slightly improved her chances of giving birth to more waterbenders like herself, then was it not her obligation to the tribe to join with Sokka?
Further channeling her brother, she then reasoned that regardless of what some spirits may or may not think about such a thing, was what the spirits thought really more important than the tribe? Sokka certainly wouldn't think so. He would probably say something like:
"Oh, really? Well what have these 'spirits' ever done for us?" or "Spirits? Puh-leeeaase. I don't have time for your superstitious gobbledygook. Have you guys ever even seen a spirit?" or even "Why should some magic glowy spirit guys care who you get together with? And even if they do, why should I care what they think?"
Katara giggled softly, amused by the expression she envisioned on her brother's face and the dry, sarcastic tone she could practically hear as the words ran through her head. She felt a warmth in the pit of her stomach, and smiling softly she finally returned his embrace, whispering:
"You're right," and softly kissing his forehead, before moving her hands down. She would have to remember those arguments she had come up with for later, in case she ever needed to defend what she was about to do.
Leaning back, Katara smiled at her brother and went gladly with him to one of the old, abandoned igloos at the edge of the village. The look in Sokka's eyes no longer scared or upset her. No, now it only excited her.
What happened when they went inside the old igloo?