This particular festival has the girls dressing up as brides for the gods. Nina wasn't sure what to make of Koume's Westernized flair.
Kon hadn't had much good luck with wardrobe changes recently, so she felt some trepidation with putting on this new outfit.
Chiya got into some trouble with some sweet sake (which is not supposed to have alcohol in it), which caused major problems for Saku. Nina needed to apologize, but Saku thought she was going to bare her belly like Chiya instead of the harsher seppuku.
Chiya caught a cold during her drunken adventure, so the girls brainstormed ways of keeping her company so she didn't get bored or lonely. Koume as a hot water bottle seems kind of interesting.