Suletta and Miorine are doodling on this bus, in case anyone's wondering.
Damn, beat me to it. :D
More specifically, it's an annual event done for the Ooarai Anglerfish festival. And as such, you can tell from a lot of the sketches on the bus that many of them include elements of Girls und Panzer. Omachi (slabco) also happens to be a prolific GuP artist himself.
Hold on Suletta—!Aren't these water-based magic markers! What'll I do if it disappears right after I've drawn it!B-B-B-But I'm the Mercurian Witch~!suisei no majikku - water-based magic markers
suisei no majo - Witch of Mercury
Both versions of suisei start with the kanji for water(水), and Mercury literally means "water star" in Japanese.Water-based magic marker