No Game No Life, Vol. 4 (Light Novel)

In a world where games decide everything--even national borders--a genius brother-sister duo aim to put their gamesmanship to the test...to save humanity!
Having been transported to the world of Disboard, where everything is decided by games, Sora and Shiro (who together form the unstoppable gamer team ' ') are still winning. They've racked up an unbroken string of victories against opponents armed with all manner of magic and treachery. As the pair enjoy a well-deserved vacation in the Eastern Union, they're approached by a Dhampir named Plum. Sora and Shiro prepare for battle, but this game is one of the very few they haven't beaten and mastered--the game of love!