User blog comment:Gary299/High School DxD BorN episode 4 review/@comment-75.32.233.196-20150502044537/@comment-26209278-20150502110852

It's used to as a replacement for the RG between Rias and Sona,showcasing Saji and Tsubaki. Maybe they'll have one in the future, but doubtfully.

And yes, it has been confirmed that vol.7 will be mixed with the events of 5 and 6 :)