These folks are cosplaying booth companions. While booth companions at most trade shows are decked out in skimpy clothes with a corporate logo, geek event Dream Party is a little different.
Tokyo Party is a gathering of console game developers, retailers and fans. Some, but not all, of the game developers (take UNiSONSHIFT, Navel and minori, for example) create adult PC titles. What makes Dream Party interesting is how the companies have booth companions dress up as characters from their works or as the company's "image character", instead of just putting them in a mini skirt and branding their company name on them.
For many of the companions, there is more emphasis placed on the costume design itself than making the clothes as revealing as possible.
「アフィリア・サーガ」握手会＆企業ブースで見かけたコンパニオンさん 【ドリパ東京2010春レポ】 [Moeyo.com]