Japanese free-to-play online card game developed by Kadokawa Games. The game was launched on April 23, 2013. As of May 2014, the game is available in Japan only and has 2 million registered players. The game has developed into a much larger media franchise; various
media including multiple manga series and light novels have been released, in addition to an officially licensed tabletop role-playing game. A television anime series and PlayStation Vita game have been announced.