The Ronin is a poor variation of a Samurai, after this, Zabuza could never look at them the same. Objectively, he always knew what made a Ronin dangerous was their past as a Samurai and yet he'd brought many down to their knees and lobbed their heads off for the bounty— a share of which he barely got.
However, facing a true Samurai was a different thing entirely. For one, they just loved their armour. Looking back now all those Ronin were terribly depressed and kept their sword preciously strapped by their side, very few ever managed to become Ronin and keep the armour. For Samurai it was an all day, every day uniform.
A costal fort this large had space aplenty for the many Samurai working to ensure none of the Daimyo's ships came close without being met and boarded at sea with striking immediacy. In their mission strategy the costal fort split in two sides, one watching the sea at the east and the other watching the west.
Zabuza stalked around the spacious square hosting Samurai and their keepers on the east side. There was a central kitchen for the entire base that sprawled onto each side of the fort with tables, chairs, barrels of sake and jugs of water for those breaking fast or celebrating their inevitable victory against the Daimyo.
Over the days they'd scouted and watched them, Zabuza got his head full of the enemies skewed believes. It had been years the war raged, with the first months being a slog of ally gathering and the Daimyo threatening and buying loyalty of their old barons. It progressed slowly until the 'corrupt' peace seekers were beheaded and the war renewed with certain fury, one that would not be satiated by diplomacy or courtesy but with violence and bloodshed alone.
And they thought they've won. Zabuza mused as he sauntered away from one long bench to another, presenting seated Samurai with a wash hand basin and placing their food from the tray he balanced. The fools didn't even look up at him as he gifted them their deaths, but that was alright, they weren't expecting servants to be wielding death, shinobi hadn't entered the war yet after all and thus they had nothing to fear.
Zabuza pulled away, retreating back into the kitchen as his meagre [Transformation] jutsu hid his grin and snickering under the veil and visage of some young girl he'd seen in the village nearby. He had little time setting the stage for the thinning of the Samurai with Mangetsu likely to cause havoc on the eastern side and Juzo soon to assault the Named Samurai in charge of the fort.
Chaos would soon ensue. But poisoning their breakfast was the least he could do to even the playing field, a few would die within the hour as their stomachs burst open within them and another dozen would be too crippled by the agony to raise even a toothpick in defence.
Zabuza smiled, tossed the tray into a sink and slithered out the kitchen without another person seeing his disguised person. The eastern square Juzo had placed him in charge of had its own gate; seemingly used to cart in goods bought from the populace or brought from sea with the kitchen in such short proximity. It was also large enough to contain a manned stable with near a dozen horses grazing on feed at the moment.
Losing the disguise Zabuza walked over to the gate, ignoring the singular gateman that witnessed a young lady approach only to disappear in a haze, replaced by a dreaded shinobi. Words failed to leave his throat even as Zabuza locked the gate from the inside, he uttered a single syllable and earned a gut full of iron.
Zabuza yanked his kunai free only to bury it in the voiceless man three dozen times over before letting his body drop; that was as easy as it'd get from now as the gateman was the only one without Samurai armour.
To their credit, it only took Zabuza unsheathing his wakizashi and standing expectantly with the gateman bleeding out at his feet for a minute before the entire square had eyes on him. He grinned at the attention, they murmured, not believing their eyes and as one Samurai stood to bark outrage the seeds Zabuza had sown erupted in another.
The poor Samurai coughed blood like he was a fountain, his stomach emptied itself with violent force as his brothers startled away from him only to choke on their own bloody saliva. Soon three out of every five were wailing the eruptions of their stomachs.
"Shinobi…! Kirigakure shinobi!" A single well Samurai screamed over the orchestra of agony Zabuza had unleashed. It was almost unfair to see so many crumple without testing their prowess with the blade but Zabuza had a mission to do.
"Come then! Come and kill this vile shinobi!" Zabuza taunted the few left standing, only seven Samurai had not tasted a spoon of the poison he fed their camp and one of them was fleeing to raise alarm.
He let him go with a kunai flicked into the back on his knee. That pesky Samurai armour got in the way but the injury had been dealt. His comrades roared forward, their katanas unsheathed with the rage and Zabuza welcomed them.
He parried the first and ducked under a follow up slash to jut his shorter blade through the under of the Samurai's jaw. Another shrieked in a combination of fear and anger at his brother's visceral death, his blade bore down on Zabuza along with four more of his brothers positioned to flank and skewer him.
But their blades met nothing but empty air as Zabuza leaped farther and faster than anyone of them could see. He flipped mid-air, cushioning his descent with the expectant and baffled face of a Samurai's face. He snatched his landing platform by his hair and flipped him over, armour and all.
Slammed onto the ground and disarmed the Samurai only had a chance to yelp before Zabuza's wakizashi dipped into the back of his exposed skull. Zabuza darted away as a katana brushed viciously against his hastily raised kunai; not only were the Samurai, well, Samurai, they were fully grown men to Zabuza's fourteen years, the strength gap between them was immeasurable, at least until you consider he's a shinobi.
Unleashing a flurry of senbon and the rushing Samurai, Zabuza kept fair distance between them as he watched one and then two of the five remaining Samurai ignite their katana's with chakra.
There was an idle hum of thick chakra cloaking their blades, sharpening the edge and enhancing the sheer stabbing power of the already dangerous weapon to an extreme.
"You're dead, shinobi!" The two chakra ready Samurai lead the charge, their weapons held away as they dashed forward to strike. Unfortunately for them, Zabuza had fought several Ronin who never failed to use the same kata and attack patterns these Samurai now rushed at him with.
Chakra felt at his fingertips as he backed away, the ethereal energy quickly converted into droplets of water he flung the eyes of his charging foes. Once shut, Zabuza lurched underneath the decapitating slash of the second Samurai and delved into the blinded Samurai's guard with his wakizashi impaling through the man's jaw.
"Raaa! Die you fiend!" The second pivoted and came down on Zabuza with a flurry of slashes and thrusts he didn't dare parry with his bare wakizashi. A chakra enhanced blade grinding away his dear short sword's steel is the last thing he wanted. "Join me brothers!"
The Samurai yelled for his fear stricken comrades to wake up and fight, but Zabuza's grin and hungry glare kept them at bay, hesitant. One already fought to pry the gate open and another simply stood in watchful terror.
Zabuza's fingers flipped through hand seals and the raging Samurai halted his charge— the first smart thing any of them had done— and promptly turned his back to Zabuza as he fled from the wrath of a shinobi's jutsu.
Except, there wasn't so much as a splash of water, rather blood sprayed from the man's headless neck as Zabuza set his head free with the rapid application of the [Body Flicker] jutsu.
Zabuza turned his gaze, two Samurai remained and one was deathly terrified of him and the other was already looking to flee. He licked his lips and got ready to execute them when a flood of water rushed through the kitchen corridor, soared over the inner wall and lapped at their feet. The water was bloodstained and carried more than a couple corpses in it.
He snorted. Hozuki and their fancy Ninjutsu. Mangetsu was on the other side dispatching enemies as well. Zabuza flicked a senbon at the frozen Samurai, thanks to his stillness he managed to get it through the few crevasses in their armour and a moment later the man fell face first into the water.
All that was left was the coward and Zabuza would be free to go over and show Mangetsu how a true shinobi got rid of his enemies.