User blog comment:TheRealUchihaItachi/Wait wait wait wait.... Hinata is Yozora's sister!!!??/@comment-5714902-20140120075413

Yes, Hinata is Yozora's older sister, I'm a lightnovel fan and haven't watch the anime so I don't know if it had been mentioned in the second season or not but this was revealed in the Volume 9 of the lightnovel.