When I looked at Mei Ling and Flandre, the first thing I thought of was a soldier saying goodbye to his daughter as he goes off to war (and Mei Ling's uniform-looking outfit sends it) and the fact the characters' eyes are shaded out gives off a serious or ominous impression. But the way Patchouli and Koakuma's are dressed kinda quash that.
Maybe more realistically, it looks like Patchouli and Koakuma are off to some magicians' guild/academy to learn/teach and brought Mei Ling along as a guard... or something.
My initial impression was that they were on their way to a funeral, but Meiling's expression is all wrong for that and they wouldn't be taking suitcases, so... I got nothin'.