No Game No Life, Vol. 9 (light novel)

All's fair in love and war! Gamer siblings Sora and Shiro have at last defeated the Old Deus Holou, and now they're switching gears: Their next endeavor is to make Holou the number one pop idol in all of Disboard! They've even abandoned their royal posts, halting all domestic affairs to focus on her training. But amidst the chaos of their pet project comes a strange message from the representative of the tenth-ranked race, the Ex Machina... Is another arduous battle on the horizon for Sora and Shiro?!