Board Thread:Speculation House/@comment-68.186.83.101-20130601225528/@comment-4010415-20160120151729

It definitely helps that Ruby and Yang didn't know that Summer wasn't Yang's real mother until after Summer died, so at first, they grew up thinking that they were both fully sisters and that Qrow was the uncle of both of them.

When Summer died, Ruby and Yang were old enough to remember her. Ruby said to Summer's grave "I miss you too", but you can't miss someone you don't remember. If she didn't remember Summer, she would've said something like "I wish I could meet you" or something.

So, Ruby got a close bond with Qrow before Summer died, due to thinking that he really was her uncle. After that, she still kept the close bond, considering that it seems like Qrow has been around Ruby and Yang a lot whenever he wasn't on missions. He treats Ruby as if she really is his niece and shows that he loves her as much as he loves Yang. It's hard not to love someone like family when they treat you like family.