After more than three weeks at the top of the Android top grossing charts, DeNA has brought its hit Rage of Bahamut to the U.S. iTunes App Store. It’s a sign that the long-delayed iOS version of the Mobage platform — originally scheduled to come out sometime in either November or December 2011 — is finally ready.

The arrivial of the Japanese-developed game, which has so far been DeNA’s biggest hit in North America, sets the company up to compete on an equal footing with arch-rival GREE on iOS. In its most recent earnings call, GREE revealed its long-anticipated global mobile-social gaming platform will go live in 153 countries at the end of May.

Even without its network ready, GREE has seen some early success on iOS with its first North American-developed game Zombie Jombie. The title has been downloaded more than 1 million times and has recently surged up to the No. 17 spot on the top grossing iOS apps chart.

Both Zombie Jombie and Rage of Bahamut are card-battle games, a genre that has proven to be extremely popular and lucrative in Japan. According to industry watcher Dr. Serkan Toto, during the past year at least 50 percent of the top grossing games on both the GREE and Mobage networks have been card-battle games. While it remains to be seen if the genre will see the same success in North America, so far both games are off to solid starts.

There are now six Mobage games on iOS, four of which — Ninja Royale, Dreamtopia, Magical world of Decotower and Rage of Bahamut — are less than a month old.