"No Game No Life" volume 6 by Kamiya Yuu. Actually, this is volume 0, backstory to how the current world came about.
This volume is in a very different tone from all previous volumes. In contrast to the relatively small scale games before, this volume consists of one planet scale war, with very few victories and lots of casualties. The two main characters for this volume are very similar to Sora and Shiro in personality, but endured a decidedly less pleasant life in comparison. Whereas Sora managed to win a fair bit even while taking high risks, Riku mostly managed to not lose by making lots of sacrifices.
The highlight of this volume is the introduction of the Ex Machina race, a networked collective capable of inventing counterattack measures almost instantly. It's rare to see this kind of technology in a fantasy world setting, although I suspect the author did it because this volume called for massive deaths, and it was morally more acceptable for machines to die rather than humans. Thanks to Ex Machina and others who sacrificed for Riku's master plan, the war did end, and the "No Game No Life" world 6000 years later is more enjoyable.
It would seem wise to not read volume 6, for now. Recall that volume 2 ended in a cliffhanger that was resolved in volume 3, and volume 4 ended in another cliffhanger that got resolved in volume 5. Seeing this pattern, I was wondering if I should let volume 6 sit on the shelf and wait for volume 7 to be released first. Eventually I gave in, but I should have waited -- not because of another cliffhanger, but because I am not sure if all this depressing history would be relevant later on. We wouldn't know until volume 7 is released. I do hope that volume 7 would be a lot more cheerful.
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