Invaders of the Rokujouma!? Collector's Edition 6 (Light Novel)

Contains Volumes 15-17!
Deciding they need a bit of a break, Koutarou takes the girls out for a day of beetle hunting. An unexpected reunion, however, leads Kiriha to realize there's more than just beetles hiding in the mountains outside of Kisshouharukaze City...
With things coming to a head between the radical and conservative factions, it's finally time for Kiriha to take up arms for what she believes is right. With both the underground and the surface at risk, however, can anyone really win in this fight?
Things are finally peaceful around Corona House again, meaning it's time to kick back and have a little summer fun! There's swimming, volleyball, a test of courage, fireworks, a rollercoaster, a whole mountain of homework, and... a surprise visitor?