Checkmate

Sora and Shiro are siblings, and they both have distinction as outstanding NEET (Not in Education, Employment, or Training) hikikomori gamers. Their skillfulness have even spawned urban legends all over the Internet. Unfortunately, these two gamers consider the real world to be just another "crappy game," and end up having the shock of a lifetime when they are summoned by a God named "Tet" to an alternate world.

There, Tet has prohibited hostility 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 whose lives are all about gaming, become the "Saviors of Humanity" in this alternate world?