User blog comment:TheRealUchihaItachi/Wait wait wait wait.... Hinata is Yozora's sister!!!??/@comment-211.25.214.52-20140120152527/@comment-211.25.214.52-20140121152310

That info came from the novel (volume 9). I read them at some summary from pastebin and animesuki forum since baka-tsuki hasn't translate them yet.