Sentou Yousei Shoujo Tasukete! Mave-chan

戦闘せんとー妖精よーせい少女しょーじょ たすけて！！メイヴちゃん

Rei goes to an anime convention and ends up in a world created by the desires of anime fans. Rei doesn't know how to get back and the world starts to collapse because the convention is coming to a close.