Their “extremely noisy” YouTube videos usually show them playing Mario Kart and goofing around, but two Ukrainian brothers are now using their popular Japanese-language channel to speak out against war. Sava Tkachov, 26, and his brother Yan, 20, have 1.26 million subscribers on their channel Sawayan Games, where most videos are introduced by Sava shouting and gesticulating wildly in sunglasses and chunky headphones. Now the brothers, who were brought up and live in Japan, have used their platform to raise 3.6 million yen ($29,000) in donations for Ukraine since Russia launched its bloody invas…