User blog comment:Psogen/12th Squad/@comment-11051098-20140928120013

Kisuke gave Mayuri the position as Vice President - or Lieutenant position - in the SRDI itself. In the 12th Division, Mayuri was the 3rd seat and Hiyori had the Lieutenant position.

I don't know which chapters cover the Turn Back The Pendulum mini-arc where this is from, so I can't check it in the manga, but as far as the anime goes, the information from episode 209 is correct.