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 invasion last month.

Fans have left comments of support on their videos, which are tagged with the #NoWar slogan and mix gaming commentary with information and appeals to help Ukraine.

Since the invasion began, social networks like TikTok have come alive with images posted by young Ukrainians of newly trained soldiers and life in underground bunkers.

Sava said on Thursday that he hoped the pair's videos could pack a similar emotional punch.

"The kind of information I'm sharing is very direct information from my father or his friends (in Ukraine), and I'm sharing that instantly, in a very direct and real way, in a personal way," he told reporters.

"It's something that can hit viewers right in the heart," he said.

Sava, a basketball player, moved to Japan aged four when his father began work there as a business consultant. Yan, currently a student, was born in Japan.

Most of the pair's followers are young Japanese men
Most of the pair's followers are young Japanese men AFP / Kazuhiro NOGI

The brothers started their gaming channel two years ago, and say most of their subscribers are young Japanese men, with the majority aged 24 or under.

"It's extremely noisy, so please refrain from watching it before going to bed," says the channel's description.

In one recent livestream, Sava appeared with animated angel wings in the yellow and blue of the Ukrainian flag.

The pair have also posted less-than-subtle protest skits, such as whacking a photo of Russian President Vladimir Putin in time to music.

Sava was initially "conflicted" about mixing political commentary with gaming, Yan said.

"But he thought by using such familiar content, like games, it might be possible to reach more people, and particularly more young people."

And commenters have been weighing in, with one writing: "Although it's a painful time, I think the Sawayans' attitude is definitely reaching people all around the world. I'm only a high school student... but I want to do what I can. No war."

The pair, who speak Japanese, Ukrainian, Russian and English, said they feel strongly attached to Ukraine despite having only visited a few times.

"Ukrainian soldiers the same age as me are being killed," said Yan.

It's easy to turn your eyes away from reality. But the question is, do you face up to the problem, or do you stand back, as a bystander? And it is up to you to decide."