I regret that my story offended you. I wonder whether you are also offended by Saiyuki canon, which (if I may also state the obvious) features several incestuous relationship between close biological relatives... which, incidentally, Gojyo and Ataeko are not. Also, Ataeko is 12 when Gojyo finds her.

Still, I'm not going to argue ethics; for any relationship in the real world, I would agree with you. But the story does not deliver moral judgement of any kind - that is not its intent. This is a story set in a fictional world, a world that explicitly includes incestuous relationships. The relationship between Gojyo and Ataeko is intended to echo certain canon relationships. That is all.