Uchiha Sora had no reason to refuse the Fourth Kazekage's proposal.
Once the Fourth Kazekage's confidant left, Uchiha Sora immediately began making arrangements.
First, he dispatched additional ninja to defend the border with the Land of Earth.
Since the Land of Lightning did not directly border the Land of Grass, its ninja had three possible routes of attack.
The first was to attack through the border between the Land of Fire and the Land of Grass. This required negotiating with the Land of Fire and securing Konoha's cooperation.
Konoha and Kumogakure had clashed just a few years earlier, so there was no chance Konoha would agree.
The second was to pass through the neutral Land of Iron, enter the former Land of Waterfalls, and then fight their way to Kusagakure. This route also required the consent of the Land of Iron's samurai.
Clearly, the neutral samurai would not agree to the Land of Lightning's request.
The third was to attack through the Land of Earth's borders with the Land of Grass and the former Land of Waterfalls. This required the Land of Earth's consent.
The Land of Earth had recently suffered defeat at Uchiha Sora's hands, so it would certainly be happy to see the Land of Lightning go to war with him.
Thus, it was virtually certain that the Land of Lightning would attack through the border between the Land of Grass and the Land of Earth.
Uchiha Sora could hardly have made a better decision than sending more ninja to defend the border with the Land of Earth.
Yet the attack from Kumogakure never came.
Because just as Kumogakure's ninja entered the Land of Earth...
The missing Eight-Tails Jinchuriki, Killer B, actually returned to Kumogakure!
The Fourth Raikage, who had been burning with rage and ready to unleash