User blog comment:B214/Season 3 confirmed!!!!!!/@comment-24.104.16.50-20150403233147/@comment-27989561-20150404070633

You should read them asap, vol 10 - 11 and 12 are amazing.

Ravel does play an important role later on, i won't spoil you.

Don't worry, the relationship between issei and rias grows a lot in future volumes, i can't spoil you.