Two words: fan service. Queen's Blade not only features some of the most famous females from frighting games, it features them in revealing poses. So you can imagine what Queen's Blade cosplay looks like.
Queen's Blade was originally a Lost Worlds style "combat picture book game" and has been published in Japan for the last couple of years. Queen's Blade features only female characters, and its spin-off series Queen's Gate has showcased the likes of Iroha (Samurai Shodow), Mai Shiranui (The King of Fighters) and Dizzy (Guilty Gear).
It has gone on to spin off a slew of figurines as well as video games.
The annual "Queen's Blade Matsuri", or "festival", was held in Akihabara. Fans gathered to battle each other in card ganes, buy lewd Queen's Blade goods and ogle Queen's Blade cosplayers.
If you are wondering if that is a small child you see with a cosplayer, it appears that it is. That, or a very short adult dressed as one. You never know with these cosplayers.
「クイーンズブレイド祭 in AKIBA 2011」イベントレポート [Moeyo!]