Petanko idol Nagi, of Kannagi, can be found cosplaying various popular characters in these official illustrations, due to be distributed as telephone cards with the limited edition of the first volume of the DVD, at certain shops.
From the left, they are: Animate (Miku), Sofmap (Niagi), Anibro Gamers (Saber), Tora no Ana (Arcueid of Tsukihime). The limited edition also comes with a drama CD, extra images, posters, commentary, etc.
Another interesting Kannagi illustration for later:
It would make sense if it said “¥100 a confession (Zange)”, but what it actually says is “Zange-chan ¥100 a go”. Interpreting this is left to you.
Putting all this into context, Akiba shops have lately been desperately pursuing such promotional measures in the face of competition from Internet retailers.
For some reason customers just don’t see the need to traipse half way accross Tokyo to pack themselves into a grotty little shops and pay mediocre prices for goods they can order online for a quarter less. Who would have thought?
On an unrelated note, otherwise nondescript technical instrument company NewOpto have also decided to dress their mascot as Nagi; apparently they have a tradition of having her cosplay various characters:
They seem to be very much the otaku company: