The Valvrave the Liberator official Twitter account has announced that the powerful duo of T.M Revolution and Mizuki Nana will be together again for the anime's second season opening theme in October.
Nishikawa Takanori of TM Revolution replied back saying, "Revolution returns!" to the news. More details to be expected from the anime's official site, hopefully soon.
In the meantime, the official site is also giving away a new L-Elf PC wallpaper here.