He appears dressed in military-style camouflage and a red beret, a Ukrainian teenager praising Russian soldiers for their courage and pledging loyalty to Vladimir Putin.
"We made our historic choice to be together with Russia," he says in one video.
"I don't give a f*** what they think about me back in Ukraine," he says in another.
For a time, Denys Kostev was the poster boy for Russia, appearing in multiple video clips as the young, charismatic face of Moscow's propaganda machine.
Now safely back in Ukraine, he tells Foreign Correspondent how he, like thousands of Ukrainian children, was systematically brainwashed and drafted into the Russian military after his Ukrainian town was occupied.
"It's a system that shapes children's minds and ideology over many years. Russia knows how to do this. They have manuals for it."
'They brainwash you'
When Russian tanks first rolled into his hometown in 2022, Denys was posting patriotic videos about Ukraine on TikTok and cursing President Vladimir Putin.
He was living in an orphanage in the southern Ukrainian city of Kherson.
At first, he says, he didn't believe the war had started. Only when a shell landed 500 metres from his bedroom did he realise it was real.
As the frontline drew closer, Russian soldiers began visiting the orphanage.
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The centre's director feared for their safety, as children had already been taken from other orphanages across Ukraine's occupied territories.
He asked family and friends to take them in.
Denys moved in with his brother and their grandmother, but within a few months, the 16-year-old was moved against his will to a youth camp in Russian-annexed Crimea.
When he protested, the Russian authorities told him they would send guys with machine guns to his home.
"It was mandatory," he says. "Especially for orphan children in occupied territory, there are no rights."
When the buses arrived, Denys and his friends from the orphanage knew they had no choice.
They became some of the tens of thousands of Ukrainian children Russia has stolen, deported or forcibly transferred since its full-scale invasion in 2022.
What he experienced at the youth camp was chilling.
"It was more of an ideological re-education camp," he says.
"First, they brainwash you with Russian songs, with some lessons about courage. They tell stories about great military prowess in war.
"Ukrainian symbols, Ukrainian music, the Ukrainian language, everything that in principle relates to Ukraine, is [was] forbidden here."
This was the start of Denys's nightmare passage through Russia's system of indoctrination and military training, which took him dangerously close to being enlisted in Moscow's army to fight against his own people.
"These are not summer camps where kids are playing in the pool or going to the beach," says Paige Farrenkopf, who leads a global team of investigators from Yale University's Humanitarian Research Lab tracking children stolen by Russia.
"These summer camps are a lot more sinister. Kids are told that Ukraine no longer exists. This is not only a mass abduction, this is a mass indoctrination.
"They are exposing kids to military training, and this is something that has continued to evolve over the last four and a half years."
Escape to Ukraine
By winter, Denys was moved back to Russian-occupied Ukraine, which is when he was signed up to Moscow's "Young Army" cadets and the military training started.
"Special forces and other military personnel came. They taught us how to disassemble and assemble, mostly the Kalashnikov rifle," Denys says.
"They taught us to shoot from different positions, sitting, lying, and standing."
As time went by, Denys started appearing in multiple propaganda videos on pro-Kremlin channels.
In one, he declared, "we feel the support of our president Vladimir Vladimirovich Putin."
His rapid transformation from a Ukrainian patriot to a flag-waving Russian appeared to be a victory for Moscow.
It was valuable ammunition for the Kremlin's propaganda machine, bolstering its narrative that Ukrainian children belong to Russia.
"They play on the idea that … 'Ukraine abandoned you, Ukraine doesn't need you, here you are needed.' It's all psychology," he says.
"And when you are already in despair, you no longer understand what to do and you are ready for anything. This works very strongly on orphans."
Denys was issued a Russian passport. It all became very real when he turned 18 and a conscription letter arrived.
"I understood that for me this was it, this was the end. If I don't leave, then I will go to serve in the army … and they will force me to kill my own people," he says.
"I really didn't want that."
After a two-year ordeal inside Russia's propaganda machine, he made a secret escape through Belarus before finally making it back to Kyiv.
Paige Farrenkopf's team has traced Ukrainian children to 210 locations across Russia and occupied territories, but they estimate there are hundreds more.
She says it's now a "race against time" to rescue those at risk of being drafted into Russia's military machine.
"These kids are getting older. These kids are being enrolled in Russia's military, and the more time that goes on, the harder these kids are to identify and return," she says.
"Kids should not pay the price of adult wars."
