Board Thread:General Discussion/@comment-9991778-20130601230059/@comment-80.89.94.21-20130603113128

I think that Yang might have been Ruby's mentor at the Insitution/School during her freshman year and the two became good friends - hence 'Sis' ("Nee-chan"). My head-canon also wonders if Yang might have been Ruby's shoulder to cry on after the death that led to the building of the memorial we see at the beginning of the Red Trailer.

BenRG on roosterteeth.com