Facebook, we are told, has a monetization problem on mobile. For ideas, it might want to look no farther than a Japanese company called GREE, which was something of a favorite at the E3 technology show. One of its popular games alone makes the company 200 million dollars each months, reports the BBC. In Japan, it’s bigger than Facebook—indeed, it’s the largest social network in Japan, period. What exactly is GREE? We tend to think of Zynga games as something that happen within a social network like Facebook. GREE almost turns that equation on its head; the games come first, and the social features like chatting all occur within the game. The games are the social network. And it’s all on mobile—GREE saw that wave from the distance. “We’re in the post-PC era already in Japan,” GREE’s CEO told the Guardian. “Our experience in the mobile arena far exceeds Zynga’s,” he added. Zynga—and Facebook—better watch out. Not satisfied to merely dominate Japan, GREE is branching out to Western audiences. It’s been snapping up other social gaming companies left and right—most recently, Funzio, which makes popular graphical RPGs. It shelled out $210 million on the deal, reported TechCrunch. The year before, it had paid $104 million for a gaming network called OpenFeint. The company launched its first US-made game in March. It’s called Zombie Jombie.