User blog comment:B214/Season 3 confirmed!!!!!!/@comment-24.104.16.162-20150329163637/@comment-1359322-20150331112202

You're misunderstanding something here, Rias is only a replacement for Sirzechs who couldn't become the heir, that's why Millicas is the next head after Rias, because the rightful clan head lineage is from Sirzechs not Rias.