Who did Sue cosplay as in Genshiken Nidaime episode 9? Who did Sue cosplay as in Genshiken Nidaime episode 9? It looks a bit like Canaria from Rozen Maiden, except the doll doesn't have a crown.
The outfit is almost identical to one of the outfits of Meruru (or, more properly, Princess Merururinsu Rede Arls), the titular character of the popular JRPG Atelier Meruru. Here's a comparison of the two. 

Sue (ignore the fact that the background is stitched together):



Meruru in her Alchemist costume:



I don't think I need to point out the similarities, but in particular the design of the skirt, the straps on the front of the dress, the wand, the bow on the neck, the crown, the hair style, and the flowers on the outfit are all the same.

In addition, it seems that Sue's dialogue of the episode references Meruru, so there's no doubt that this is who Sue was cosplaying as.