The theme for this set of images is that they were drawing numbers on each other's face, counting down to the release of Nachuyachumi+ Episode 1.
Going by the crayon that each of them will be holding in the following images: Ayano drew the "8" on Chitose's cheek. Kyouko drew the "7" on Ayano's cheek. Yui drew the "6" on Kyouko's cheek. And so on, in that fashion.
with Chitose drawing the 1 on Akari and Sakurako using a permanente marker on Himawari instead of an easily-washable crayon because of course she had to do something like that.