Sengoku stood frozen in the training ground, his mind racing as the Jonin's words took root.
Monzaemon's advice wasn't about designing a complex rapid-fire mechanism; it was about shifting the paradigm entirely. He had suggested turning a single-use expendable into a reusable, tethered weapon.
The shift in perspective was illuminating, but as Sengoku quickly realized, the practical execution was riddled with engineering nightmares.
The first hurdle was the tether itself. He needed a physical wire that was microscopically thin, yet durable enough to withstand the explosive kinetic force of the spring-loaded launch. Standard chakra threads wouldn't work—they were intangible energy constructs that required a constant feed to maintain tension. Sunagakure was rich in mineral deposits; perhaps a specialized, ultra-fine metal alloy existed? But that led straight into his crippling financial reality. Merely building one crude prototype had drained his savings. How could he afford specialized, weapons-grade wire?
The second hurdle was the anchor point. Even if he procured the perfect wire, how could he reliably secure it to the flat tail of a three-centimeter senbon? Micro-drilling?
Yet, if he could somehow solve these issues, the tactical applications were staggering.
The fired needles wouldn't just be projectiles; they would become physical extensions of his chakra network. A senbon embedded in an enemy's clothing could be violently yanked to destroy their balance at a critical moment. Needles driven into walls or trees could instantly be pulled taut, weaving an invisible network of tripwires. The tiny Hover Drone would instantly evolve from a simple ranged weapon into a multi-layered tool for crowd control, spatial disruption, and assassination.
But all of this hinged on finding that miraculous thread, solving the anchor problem, and mastering the terrifying level of micromanagement required. He would have to suspend the drone in mid-air, trigger the launch, and actively manipulate twenty independent, nearly invisible wires simultaneously.
Driven by the sheer potential of the idea, Sengoku packed up his gear. He had to find the right materials.
A month passed.
Sengoku sat cross-legged in the center of his stone house. The floor around him was littered with scattered senbon, heavily modified blueprints, and a small spool of material that shimmered with a faint, metallic luster: Kazekage Spider Silk. Purchasing that single spool had entirely drained a full month of his academy stipend.
Over the past thirty days, he had poured every waking hour into realizing Monzaemon's concept. Through grueling trial and error, he had finally cracked the attachment method, securing the silk to the base of the needles.
But the moment he moved to practical testing, the harsh, unforgiving reality of combat shattered the theory.
The mental burden was catastrophic. Hovering the iron sphere, timing the launch, and then attempting to consciously guide twenty microscopic threads through the air required an impossible split of focus. A single test run left his mind pounding with exhaustion. In a high-speed, life-or-death battle, that kind of distraction was tantamount to suicide.
Furthermore, the physical retrieval was a disaster. When he yanked the silk to pull the needles back, they didn't neatly slide back into their firing chambers. They violently clustered together, tangling into a hopeless, jagged knot of razor-sharp steel and microscopic thread. Untangling and reloading them manually took just as long as loading fresh ammunition.
Sengoku stared at the cost breakdown scrawled on his drafting paper. The price of the Kazekage Spider Silk vastly exceeded the combined cost of the iron shell, the spring mechanism, and the senbon payload.
Monzaemon's advice had come from a place of genuine expertise, but it possessed a fundamental blind spot: Monzaemon was a Jonin. He viewed engineering through the lens of a veteran with vast chakra reserves and a substantial military budget. He had absolutely no concept of the crippling limitations faced by a seven-year-old orphan relying on a meager village allowance.
Sengoku rubbed his temples, a sudden, radical shift altering his perspective.
'If the puppet itself is so cheap to make... why shouldn't it be disposable?'
The shell was just scrap iron. The firing mechanism was a basic tension spring. Why was he trying to turn a cheap, mass-produced tool into a fragile luxury weapon?
'Think about explosive tags,' he realized, his eyes widening slightly.
Explosive tags were strictly single-use. Yet, shinobi burned through them without a second thought because the tactical payout—killing an enemy or destroying cover—vastly outweighed the financial cost. Why should his drones be any different?
He had been forcing himself into a corner, obsessed with the traditional puppeteer's mindset of preserving the weapon at all costs. But the core essence of tactics was neutralizing the target, not saving the tool. If the damage inflicted was absolute, a single-use weapon was the most efficient choice possible.
The moment he accepted this brutal, pragmatic truth, the "insurmountable" engineering hurdles vanished into thin air.
He didn't need a complex retrieval mechanism. He didn't need expensive Kazekage Spider Silk. He didn't need the suicidal mental burden of multi-thread micromanagement.
All he needed was absolute, concentrated destruction.
He could simplify the internal structure to its absolute baseline. He could hammer the iron shell thinner, making it lighter and cheaper. Better yet, he could create a dual-layered shell and pack the hollow space with cheap steel ball bearings to maximize the blast radius.
The expensive, polished senbon could be discarded entirely, replaced by crude, triangular steel spikes—heavier, cheaper, and infinitely more devastating upon impact.
Calculated this way, the production cost of a single drone would plummet to a fraction of the price of a standard explosive tag.
His tactical approach shifted completely. He wouldn't bother with fancy tripwires or reusable volleys. He would simply carry ten or twenty of them, swarm the enemy, fly the drones directly into their faces, and trigger the payloads at point-blank range like hovering fragmentation grenades.
"Heh..."
A soft, self-deprecating chuckle escaped Sengoku's lips, dissipating into the cool air of the stone house. He had nearly bankrupted himself trying to be elegant.
He carefully rolled up the spool of expensive Kazekage Spider Silk and tucked it away in his pouch; it might prove useful for a different project in the future.
Sweeping the failed, complicated blueprints aside, Sengoku pulled a fresh sheet of paper toward him. His pen flew across the page, drafting a new schematic for the Hover Drone.
This one was devoid of any elegance. It was simple, crude, and devastatingly lethal.