Naruto's actions during Chapter 50, if you were curious.
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Naruto was the first one to notice Yukie. It totally makes sense, since there's only one of Shikako and Sasuke, whereas there's at least twenty of him in the fight, and that makes him the most likely one to see her anyway, except Naruto is kinda, sorta keeping an extra eye on her because he promised to keep her safe and she kinda freaked out in the last fight.
It's not like Naruto doesn't understand. He's freaked out about a few fights himself and Yukie would probably be better off if she had an awesome team to watch her back, because that helps, it help a lot, and Naruto knows because he trusts his team to watch his back - even Sasuke, who isn't as much of a bastard as he thought, way back at the Academy.
So he was keeping an extra eye on her, which was kinda hard because he had to keep an eye on Sasuke and Shikako as well, and keep fighting and he's pretty sure that without Shadow Clones he wouldn't have been able to manage it at all.
So when Yukie steps forward, hesitant and jerky, face about the same shade of white as the snow, instead of hiding with the actors like she's supposed to be, Naruto knows that something is about to go wrong.
Has already gone wrong.
"Yukie!" He shouts, because the snow ninja have already seen her and maybe if she just runs… "What are you doing?"
She lifts her chin in defiance, but against him and not them, which is weird and just… it's just wrong. She's wrong.
"If you keep fighting, you will die," she says. "Just go home."
"No!" He snarls, and it seems to surprise her a lot. Naruto summons more clones, orange flooding the area around him and tries to reach her.
"I am what they want," she says. "If I go, the fighting will stop."
"That's your solution?" He scoffs. "Old man Sandayuu isn't just going to give up, just because you do. We won't give up."
The pink haired snow ninja, the one they fought before, on the ice, pelts him with ice shards that impact heavily on the ground. He has to dodge, and when it's over, she has Yukie scooped up into her arms and is running for the train.
As she runs, she kicks a discarded kunai and it explodes into chakra smoke, unnoticed by anyone. But the reminder strikes deep into the back of Naruto's brain, past the anger and confusion, and hits straight into his determination. It takes seconds to transform himself, and a clone plucks him out of the air even before he falls. It feels weird to be a kunai, and weirder to be thrown, but he's done it before and it isn't hard.
The girl carrying Yukie darts inside the open door and he is thankful for the pure brilliance of his clones throw. He doesn't want to hit her, in case he gets Yukie, and that weird armour might drain his chakra and wreck the transformation. That would be bad. But he needs to get on the train.
The sharp edge of his blade slices her shoulder as she clears the door and throws herself to the side as soon as she is in, and he and ten identical kunai impact the wall of the cabin.
The thud echoes inside his not-head and he kinda wants to groan. It doesn't hurt, exactly, but it still doesn't feel nice.
"Close one, Fubuki," the blue haired guy that was fighting Kakashi-sensei says. He sounds kinda amused, which is a jerk thing to do when your team mate nearly gets stabbed.
Fubuki scoffs. "Like you weren't getting your ass kicked by Hatake."
The train starts moving, slowly at first then faster, and their banter is cut off when someone else clears his throat. "It's been ten years, Koyuki. Let me see your face."
That must be Dotou. He doesn't really look all that special, as far as Naruto can tell, with a flat, wide face and squished nose. But he's dressed in a heavy fancy kimono thing that looks pretty expensive from what Naruto's inexperienced eye can tell.
Yukie stands silently. She looks kinda small and scared, and Naruto wants to leap down there and help her. Except, he knows how good those three ninja down there are and even he doesn't think it's really going to work. And so no matter how much it burns - burns like sitting out his own fight in the Finals - he has to wait.
His team is fine, he knows, because his clones have just finished dispelling. He wished at least one stuck around so he could tell them where he is now, but he's pretty confident they'll know. And he can't use jutsu in here, so it's not like he could reply but still…
"Do you have the hexagonal crystal?" Dotou asks.
"Yes," Yukie says. Lying might not have helped very much, but Naruto is pretty damn sure he wouldn't have just admitted it.
"Good," Dotou says, sounding satisfied. "That crystal is the only thing that connects the Kazahana family as a whole. It's the key to the treasure."
That look… that look Naruto immediately dubs the 'crazy face'.
"A key?" Yukie asks, voice quiet.
"When I took over this country from your father, there was nothing left of the Kazahana family." Dotou starts pacing, short movements up and down the train car. "Sousetsu must have kept the treasure elsewhere. I looked for it and I finally found it. It's a massive weapon hidden in the Rainbow Glaciers. And I have found a keyhole that fits the hexagonal crystal. If I get a hold of the Kazahana weapon, our country will have the power to overcome the five shinobi countries!"
It isn't really anything that Kakashi-sensei hasn't told them, except more real. That guy is a jerk, killing his brother just for some treasure. Some things, Naruto will never understand.
"A weapon…" Yukie says, eyes sinking down. "I see…"
"Will you hand it over, Koyuki?" Dotou asks. It isn't really a choice. If she says no, they'll just take it anyway.
Her hands twitch for a moment, before coming up and undoing the clasp at the back of her neck. She doesn't look up, not once.
Dotou takes it, but his glee vanishes into anger. "Don't try and fool me! This is just a fake!"
Yukie jerks. Naruto is kinda surprised too. "A fake? But I…" She swallows. "Kakashi Hatake."
Okay, now Naruto is lost.
"I see. He'd be able to switch it easily," Nadare says. "Should we return and fetch him?" He doesn't look that keen on the idea, and no wonder, because Kakashi-sensei was kicking his ass.
Dotou considers it, hand still clenched around the fake crystal. "They'll come after us," he says. "Be ready for him."
Naruto isn't going to let them trap his team. So he'll just have to trap their trap.
Or something.
Yukie looks like she's torn between hopeful and afraid, and the train is still rocking and no one is speaking so Naruto hunkers down to plan.
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The dungeons are freezing and dark and pretty much stereotypical dungeon. Naruto has clone spiders sneaking all around the castle, finding the ninja and exits and windows so he can get out.
He'll get Yukie, and they'll get out of here and meet up with Kakashi-sensei and then they'll work out what to do about the crystal and the weapon and Dotou…
Well, anyway. First Naruto has to get them out of here.
Finding Yukie isn't hard. Naruto is pretty sure she's made to be obvious. Which makes sense because duh, what's a trap without bait.
There are guards around, but not obviously around, so Naruto thinks he's got a bit of leeway.
"Sssh!" He hisses, before slinking out in front of her cell.
She starts but doesn't scream, which is good. Naruto starts investigating the lock, but its papered over with some kind of seal. He doesn't touch it, because if there's one thing that being on a team with Shikako has taught him, it's that seals can hurt. A lot.
"I…" Yukie stutters. "I thought that, if I just gave it to him, the fighting would end. But all he wants is to fight more…" She sounds completely miserable.
"He's a jerk," Naruto says, confident but quiet. He could maybe break one of the bars, see if she could slip out through the gap, but it would be loud and take time and there's a little voice at the back of his head that says seal, touching, bad. "You just gotta keep doing what you know is right. You can't give in to him. You see?"
She stared off into the distance. "'When Spring comes, you'll be able to see'," she quoted. "That's what my father said. 'Someday Spring will definitely come.' But there is no spring in this country. My father died, I ran away from this country and I decided to stop believing. I keep on running, and running away. I keep on telling lies, even to myself. I acted. But… for all my running, it never got me anywhere. I never… I never had anywhere to run to." She laughed bitterly, and it sounded like a sob.
"Then you just have to make spring come," Naruto said and rolled his eyes. It was so obvious. He didn't see why people just didn't get it.
Then he snapped his fingers. "I know how to get you out. Just hold still, okay?" He summoned a clone and it used the replacement jutsu to switch her out of the cell. Thankfully, there were no chakra blocking things on in the bars, or whatever, to stop him, which he totally didn't think about till after. The clone in the cell paused before dispersing itself like it was supposed to, and instead transformed itself into an identical copy of Yukie.
"Hey, good plan," Naruto said, with a nod. "Now come on, princess. Let's get out of here!"
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I don't know if I got Naruto's voice quite right, but I did want to show what he was up to while the others were chasing after him.