GEOFF BENNETT: Ukraine finds itself in a bloody stalemate on the frozen plains of the country's east and south now two years into Russia's full-scale invasion.

Russian and Ukrainian forces have taken immense losses throughout the war, and now there are calls in Kyiv for a mass mobilization.

But many people are answering their own calls to protect their nation and joining up.

Nick Schifrin and filmmaker Amanda Bailly in Kyiv introduce us to one of them.

NICK SCHIFRIN: On the stage of war, one man plays many parts.

And on the streets of Ukraine's capital, Yura is recasting himself.

YURA, Ukrainian: At some point, you're accepting your fate, and you just believe, so, like, if you should live, you will live.

If not, you will die.

NICK SCHIFRIN: Before the full-scale invasion, the 28-year-old, who asked us to withhold his last name, was a snowboard instructor, a tour guide, an I.T.

specialist, a model.

But after the invasion, he swapped the suit vest for one that stops bullets.

He translated for and drove a Human Rights Watch team into and through the horrors of war to document Russia's crimes.

War forever transforms its victims and witnesses.

YURA: When we came to Bucha, I can remember definitely the smell of rotten bodies.

It was like -- like a horror movie.

And I remember the screams of mothers who were recognizing their children.

And it was something that you cannot forget.

NICK SCHIFRIN: Nothing about this war will be forgotten.

In the center of Kyiv, the carcasses of Russian armor are rusting witnesses to Ukrainian courage.

YURA: All them burned down is because somebody just, like, in the distance of 100 or 200 meters had enough bravery and skill to shoot the rocket.

NICK SCHIFRIN: Yura says he now needs to find his own bravery.

He's tried to help the war effort in other ways.

But Russia now has military momentum.

And Yura says too many of his friends are fighting the war outmanned and increasingly outgunned.

YURA: A lot of them are already two years in this hell.

Despite the fact maybe that I don't really feeling like I'm the warrior, I need to start training and enlisting.

NICK SCHIFRIN: In January, he started basic training.

It was the first time he'd ever held a gun.

YURA: I never expected that at some point of my life I would know how to clean a gun, how to shoot a gun.

And, actually, I don't know -- now like to know this if there wouldn't be a war.

But I want to protect my country.

NICK SCHIFRIN: The country needs him.

Ukraine's army is struggling to find new recruits.

Some 15,000 have paid to leave the country illegally.

New legislation would mobilize some 400,000 more men.

Russia has more than that deployed inside Ukraine.

YURA: From our side, like, they're the best people of our country, and from their side is criminals, is people with no future.

And we are losing our best people.

NICK SCHIFRIN: Sometimes, you can forget that at night in Kyiv.

The city's bars are dark and filled with dark humor that, for Yura's friend, Slava, is an escape from the pain.

SLAVA, Friend of Yura: That's a big chance that he's probably going to die.

So, at least I hope he will give me his car or something that he have at home before he going to die.

(LAUGHTER) SLAVA: Yes.

But, actually, if we talk seriously, I'm just -- I'm just tired of losing my friends and family.

So that's my main thought about this.

I don't think that I can say anything more about this.

NICK SCHIFRIN: Loss is a terror that his mother, Natalya, hopes to never know.

Her husband was drafted.

It's hard to bear her son's choice.

NATALYA, Mother of Yura (through translator): When Yura told me he was going to, it was very hard for me to accept it, because I understand that anything could happen there.

Every mother probably feels it when she sends her children.

It is scary to send your husband, but there's nothing worse than to send your child.

QUESTION: Are you afraid?

YURA: Yes.

Yes.

Like, it's normal to be afraid.

And I'm afraid that I could die.

I could became, like, with -- like, became disabled.

It's still better than be under occupation.

A lot of guys younger than me, and, like, just giving me goose bumps about that I'm still living.

NICK SCHIFRIN: Before he leaves this all for the front, he visits the wall of heroes and the faces of thousands of Ukrainians killed fighting Russia.

YURA: Like 23 years old.

Look at this.

He's 20 years old, 24.

We do not afraid anymore, because it's kind of, we have nothing to lose, because, like, if we will lose this war, we will lose everything, our freedom, our country, our lives.

NICK SCHIFRIN: For Yura, that means there is no longer fear, only reverence for those whose sacrifice preceded his own.

For the "PBS NewsHour," I'm Nick Schifrin.