User blog comment:B214/The one-shot answer ranting/@comment-120.20.47.163-20170422142026

The answer that you have put for one is wrong as it is mentioned by Grayfia in volume 2 that Rias is the heir to the Gremory Clan.

"The woman called Grayfia picks up Buchou’s bra.

“Anyway, you are the next heiress of the House of Gremory, so please don’t show your skin to a man recklessly. Even more so if you are in the middle of this situation.” "