Any other ninja tool, and Yuji's standing in the village would have been enough to keep it for himself, he had found it, and that carried weight.
But the military music dream operated at a level that put it beyond personal ownership. Something capable of influencing the outcome of a battle was not an individual's asset.
The higher-ups would want it held by the village, available to the village, regardless of who had found it. That was inevitable.
How much it could actually do on a real battlefield still needed to be tested.
The opportunity came quickly.
Iwagakure could not absorb the insult of losing dozens of their people to a single Sunagakure boy and say nothing. Once they confirmed Yuji had crossed back into the Land of Wind, they assembled and moved. Sentry reports put the force at over a thousand.
Since his promotion to Medical Team captain, the scale of engagements Yuji had operated in had grown, from two or three hundred people to several hundred, commanding multiple Medical Squads across a full battalion's worth of coordinating units.
A battlefield of over a thousand was something he had not yet stood inside.
Shimizu received the report and the camp moved immediately, combat preparations running in parallel with the march to the border.
The two armies met on open desert near dusk.
The light was flat and cold, the wind carrying sand across the ground between the two forces as they spread across the landscape facing each other. Neither side moved immediately.
The silence had a particular texture to it.
Shimizu stepped forward from the Sunagakure line, unhurried.
"Iwate." His voice carried. "Bringing this many people into the Land of Wind, I hope you've made your peace."
Iwate had stepped out from the Iwagakure formation to meet him. The two knew each other well enough that formality between them was mostly performance.
"Don't flatter yourself," the man said, his laugh broad and deliberate. "This is just a training exercise for our troops. You really think Sunagakure can contend with Iwagakure?"
"Attacking without concealment, no preparation, no evident plan, that's not like you." Shimizu's tone shifted into something drier. "This feels rushed. Almost as though you came here for a specific reason." He paused.
"Ah. Right. One of ours killed quite a few of yours yesterday, didn't they." He let that sit for a moment. "Strange situation. Are you using us for troop training, or are we using you for practice?"
The Sunagakure ranks broke into laughter behind him.
Yuji raised an eyebrow. He had not expected this from a man whose default register was composed and serious.
The atmosphere across the Iwagakure line went noticeably heavier.
"Kill!"
Iwate didn't waste further words. The order went out and both armies surged forward across the desert, closing the distance between them like two currents colliding.
A captain turned to Ito and Sasori as the lines began to move. "Yuji's safety is yours." Then he was gone into the press.
It was not a casual instruction. Once Yuji activated the ninja tool at scale, Iwagakure would identify the source and respond immediately. He already carried a target on him from everything that had come before, the tool would make it acute.
Someone needed to be between him and whatever Iwagakure sent.
The sound of the opening exchange filled the air, jutsu detonations, the percussion of close combat, the roar of two large forces finding each other.
Yuji stood slightly toward the rear of the Sunagakure formation, eyes down.
He raised the flute and played.
The music moved through the air in waves invisible to the eye, spreading outward through both armies.
The Iwagakure shinobi still pushing through the front line began making errors, small ones at first, then compounding.
An attack landing late, a dodge that came half a step slow, a defense that opened where it should have held. The melody was working through them without their awareness, and Sunagakure's front line read the openings and cut into them without hesitation.
Some of the Iwagakure simply went down, hypnotized mid-charge, hitting the ground face-first while still moving forward.
Behind them in the Sunagakure ranks, something different was happening.
The same music that was degrading Iwagakure's coordination was pulling something upward in the Sunagakure fighters, will sharpening, movement becoming more committed, the hesitation that lived in every soldier's body during the opening of a battle burning off faster than it should have. Their morale climbed visibly.
"What is this?"
Iwate's pupils had gone tight. He scanned the field for the source and found nothing usefulm the chaos of the engagement made it impossible to isolate.
A Sensor Ninja appeared at his shoulder. "It's Yuji. The Genjutsu is his."
The name landed with an edge on it.
Their position was far enough back that the music reached them only faintly, producing a low restlessness in the chakra rather than the full effect hitting the front ranks.
But through the front line, the picture was clear, Iwagakure shinobi were falling in numbers that didn't match the engagement's balance of force.
Iwate had seen Genjutsu specialists at work across years of front-line command. What he was watching did not match anything in that experience.
Even the most accomplished Genjutsu users couldn't produce this kind of simultaneous interference across this many targets over this much ground in this little time. And it wasn't only the degradation of Iwagakure's performance, he could see the Sunagakure troops moving with more ferocity than their numbers alone explained.
The tool was working in both directions.
The Iwagakure charge squads were being pushed back and cut down along the entire front line. Not routed, but the defensive line was giving way steadily, like something that looked solid revealing itself to be thin.
"Spread the other teams out," Iwate said, keeping his voice low.
"Don't cluster, the effect travels through sound, so distance limits it. Use long-range Ninjutsu to hit the area where Yuji is positioned. Tear up the terrain, break Sunagakure's formation, and use that cover to send Hongo in deep. Prioritize taking that boy out."
"Yes."
The Sensor Ninja was gone.
Iwate watched the front line and made his own private calculation.
A Genjutsu effect at this range, regardless of the mechanism behind it, had to be drawing on significant chakra reserves. The boy was young. He almost certainly couldn't maintain it for long.
He moved forward himself to reinforce the gaps opening in the line.