Board Thread:General Discussion/@comment-9991778-20130601230059/@comment-8207536-20130602141635

202.163.162.206 wrote: Stop, just please stop before you all show that you can't read any further,

" In the Yellow trailer, Ruby encounters  Yang  and calls her "sis". However, Monty Oum has stated that this was a term of greeting and the two are in no way blood related."

This should have been apparent WITHOUT being told, considering the clear differences between the characters (the only similarities being their sex and the fact their weapons use gun ammunition, and this is shared by ALL of the RWBY team), you all should have known without starting a discussion they are clearly not related. The possibility of fraternal twins notwithstanding.

They probably aren't actually related, at least not by blood, but the outright recognition and familiarity does indicate that they 'go way back'.