|This article is about a/an events in Kamen Rider Build.|
Later, 3-on-3 Proxy Battle was fought to settle the War between Touto and Seito. In a three match campaign, Kazumi Sawatari, Ryuga Banjo and Sento Kiryu respectively fought on behalf of Touto against Rai Washio, Fu Washio and Gentoku Himuro.
1-on-1 Proxy Battle
While Yoshiko Tajimi was prepared to invade Touto despite her reprsentative's victory, she was deposed by Seito forces, which had invaded Hokuto while its military was massed at the Touto/Hokuto border, under the directive of Blood Stalk. Seito therefore fell under the control of Masakuni Mido, with Kamen Rider Grease defecting to Tout
3-on-3 Proxy Battle
While his home in Hokuto was occupied by Seito's forces, Kazumi Sawatari retained his Sclash Driver and Robot Sclashjelly, and fought on behalf of Touto as Kamen Rider Grease. Entering the first match, he was pitted against Seito's Rai Washio, youngest of the Namba Children Washio brothers who used the Gear Engine to become the Engine Bro's Kaiser. Though Engine Bro's initially overwhelmed Grease, having proved superior in prior engagements, Grease used the memory of his late comrades to perservere and strike back against Engine Bro's who was ultimately defeated.
For the second match, Touto's Ryuga Banjo, who used the Dragon Sclashjelly and Sclash Driver to become Kamen Rider Cross-Z Charge, was pitted against Seito's Fu Washio, eldest of the Washio brothers who up to that point used the Gear Remocon to become Remocon Bro's. However, as his younger brother had been defeated, Fu used his Gear Engine in the Nebula Steam Gun as well to become the combined Hell Bro's, the ultimate form of the Kaiser System. Cross-Z Charge too was initially outmatched by the Kaiser but, fighting with lessening the burden of Sento Kiryu on his mind, his fighting prowess rapidly increased and, shockingly, he was able to beat back Hell Bro's. Fu Washio, however, exploited his nature by claiming that his brother had been taken into custody following his defeat, and was scheduled to be terminated should he himself fail. Upon hearing this, Ryuga hesitated and thus provided an opening for Hell Bro's to defeat him.
With Touto and Seito having each secured a victory, the third and final match served as the decider. Sento Kiryu, using the Build Driver he had created as Takumi Katsuragi to become Kamen Rider Build, engaged Gentoku Himuro, the disgraced son of Touto Prime Minister Taizan Himuro who fought on behalf of Seito using the Sclash Driver and Crocodile Crack Fullbottle to become Kamen Rider Rogue. Realizing that only through using the dangerous Hazard Trigger could he match the power of Rogue, Sento prepared a new device that would nullify the adverse effects, the FullFull RabbitTank Bottle, which was complimented by the Fullbottle Buster. Facing Rogue in the final match, Build, through use of the FullFull RabbitTank Bottle, augmented his Hazard Body into the new RabbitRabbit Form, allowing him to fight with the power of the Hazard Trigger without the risks of losing his senses.
With the full power of the Hazard Trigger and no handicap, Build was able to swiftly overwhelm Rogue. However, Namba had arranged for Sawa Takigawa to provide him with the data for Build's new form, and once RabbitRabbit was fed by Nariaki Utsumi into the Rogue system, Gentoku was able to adapt and counteract Build. At this point, it was revealed that this was anticipated by Sento, who had realized that Sawa was spying on him, having been coerced to do so with the lives of Masahiro Nabeshima and his family at stake. Having ensured that the Nabeshima family would be saved by Kamen Rider Grease, Sento revealed that as well as RabbitRabbit, the FullFull RabbitTank Bottle could switch from Rabbit Mode to Tank Mode, allowing him to assume TankTank Form. Faced with a second form and with no data to draw from, Rogue was ultimately defeated, and Touto emerged victorious.
Immediately following the final match, Touto's Prime Minister Taizan Himuro approached his estranged son, only for Gentoku Himuro to refuse his hand and leave. Meanwhile, at the Namba Heavy Industries Ltd. branch in Seito, Prime Minister Masakuni Mido, while devastated at having lost to Touto, intended to honor his promise to relinquish his claims to Hokuto, the Fullbottles, and the Pandora Box. However, Mido's benefactor, CEO Juzaburo Namba, refused to accept these terms and, when Mido refused to go back on his promise, had him killed by Blood Stalk. With the Prime Minister dead, Namba had Stalk use his power to modify his appearance into that of the late Mido, proceeding to personally take control of Seito while preparing to unleash the full arsenal of his corporation on Touto. Due to the proxy battle not being aired nationwide, Seito and Namba Heavy Industries feigned the result of their match by publicly proclaiming Touto as the losing side and commencing their attack in spite of the agreement.