User blog comment:B214/Talk About What You Want! 3/@comment-3965848-20150420213229

I just realised something, if they do make a season after season 5 (which covers vol.11 and 12), then season 6 will also have to cover 3 volumes too. It will start with vol.14 and will need vol.15 to set the tone for vol.16.

My guess is that the extra in vol.13 that has Millicas visiting will most likely be an OVA.