User blog comment:B214/Question and Answers 3/@comment-4547267-20140921153656/@comment-24098614-20140921200238

There is a short story in the Light Novels in how Rias met Akeno because it shows how close their relationship really is because in terms of being close even though they are not related they are literally sisters in every way, and she understood Akeno's pain when she was abandoned by her family and she protected her.

Rias has never betrayed her in her life why do you think Rias lets Akeno call her by her first name without honorifics because in Japanese society because that is  a big deal because in Japan when someone lets you call them by their fist name without honorificstrust me it is a big deal because they don't usually let people do that casually.