It usually wasn't the sex that drew the three of them together. It wasn't the stimulation, or the pleasure, or the eventual climax. It was the feel of skin on skin, knowing that they could each trust the other two, that, no matter what, they would never tear into one another.
Each of the three had ended up in the seduction corps, and that was almost the beginning of everything. Certainly, the rough handling and the slow feeling of corruption that could never be cleansed was a large part of why they met as often as they could. What really drove them, though, was the feeling of worthlessness that had overshadowed each of their lives.
Sakura had always been left behind by her teammates, and even after she thought she had gained enough strength to keep up, she had found herself in the dust again. Worse, she found she had let herself fall into it. She was so weak. That was one of the reasons she'd gone into seduction, to feel that she had power, even if it was over a stranger who did not acknowledge it, and she held fast.
Ino had never really felt less than perfect before he died. She had fit in with Chouji and Shikamaru, after a time, and she was happy. After Asuma fell and Shikamaru took his, took their, revenge, she had never felt the same. She'd cried over the death, and felt weak, and that was when she remembered a whispered conversation between Kurenai and Asuma, about Kurenai's time in the seduction corps. She grabbed on to the idea as everything around her collapsed, and she ran with it.
Hinata had really, truly, loved Naruto, had felt a sense of belonging with her teammates, had dreamed of a future with a grinning husband and a lot of children. She knew her perfect future was never going to happen, though, and when her father broke the news about her betrothal, she was unsurprised, despite her improved relationship with him. She smiled and decided, after days' worth of worrying, that she would go to her husband as impurely as possible, and she jumped off into the oily abyss.
They each had their reasons, and each knew the others'. They smiled at each other as they met, usually in Sakura's apartment, and laughed through dinner. The smiles fell after the dishes were washed and they laid in bed, exhausted with the world and so, so lonely.
Sakura would comb her fingers through their hair, Hinata's soft and fine, Ino's coarse despite her daily conditionings. Ino's calloused hands would run over the other two, soft sometimes, hard others, but always gently. Hinata would breathe and lick at the other's skin, reminding all of them that they were still human, that they could still breathe.
This couldn't last forever. This wouldn't last forever. For now, though, for now it was right and they knew it as they fell asleep, clinging as tightly as they could to one another.