Invaders of the Rokujouma!? Collector's Edition 7 (Light Novel)

Contains Volumes 18-20!
Yurika comes to everyone with an unusually serious request—she wants them to help her savior and mentor, Nana. Meanwhile, children start going missing in Kisshouharukaze City. All signs point to one cause: Darkness Rainbow is back in town.
Yurika has made the bold decision to attack Darkness Rainbow’s base in order to prevent all-out war in Folsaria. Koutarou and the girls will have to consolidate all the power they have—and help from some new(?) allies—to get home safely this time.
In a collection of side stories, Yurika quits cosplay(?), Sanae and Ruth go dream diving, and Maki confronts Theia about some unexplained expenses. Then everyone participates in the school cook-off, and the results are explosive to say the least.