No Game, No Life Vol. 1 (manga)

For fans of "Sword Art Online," a brother and sister become transported into a fantasy game world and must fight to survive
The story of "No Game, No Life" centers around Sora and Shiro, a brother and sister who are brilliant (but unemployed) gamers whose Internet fame have spawned urban legends all over the Internet. One day, they are summoned by a boy named "God" to an alternate world. There, God has prohibited war and declared this to be a world where "everything is decided by games" - even national borders. Humanity has been driven back into one remaining city by the other races. Will Sora and Shiro, the good-for-nothing brother and sister, become the "Saviors of Humanity" on this alternate world?