In late July, a Korean game studio gathered roughly 250 devoted players in Southern California to mark a decade since their fantasy world first opened to Western audiences. Ten years is a long time for any shared fiction to hold its shape — long enough for a game to become a kind of home, and for its players to become something closer to a community than a customer base. The Heidel Ball was less a corporate milestone than a quiet acknowledgment that some worlds, once entered, are not easily left.