Vader lashed out with a roundhouse blow, and with his blade still locked low, Luke could only hunch down and take this one, pulling his shoulder up to partially protect himself and staggering back at the ferocity of even the glancing blow as a flare of scarlet which lit his vision.
The backward snap freed his blade though, so that as Vader powered forward to deliver another, hand closing to a fist as he pulled it to head-height, Luke swung his saber round and up in a wide one-handed arc which would have split his opponent from hip to shoulder had he not pulled hastily away.
Instead of backing up and taking a second to recover, Luke took the path he'd just cleared and darted forward, twisting to the side and dropping low beneath Vader's vision to come up close behind him, relying on his father's surprise to give him the edge.
Vader spun, lashing out with a blind horizontal sweep as he twisted round toward Luke then, as their blades met, abruptly spinning back the other way, his saber still held horizontally before him.
It was an unexpected maneuver, the first his father had sprung on him, forcing Luke to drop to a low crouch so that the blade buzzed past his head with inches to spare, his own saber in the wrong hand to parry. Vader immediately stopped his spin, using all the power in his arm to bring his saber back again, low enough to take Luke's head off.
Too close to maneuver, Luke could only bring his own blade up with no real power and allow Vader's to slide along its length towards his unprotected hand, using what little power he had to guide it just over his head, close enough that he felt the heat of its coruscating energy; heard it sizzle as it scorched the tips of his hair.
Ignoring the hiss of the blade and reaching out with the Force in that same instant he jerked Vader's legs forward, tumbling him backward as Luke reeled up and away.
.
.
Vader stumbled to catch himself before he fell, taken completely off guard and still backstepping as his son came forward, kicking nimbly off without hesitation despite his near-miss.
With all Vader's weight and momentum still moving backwards, he was dangerously split between defense and balance--and the boy knew it. He pressed in, the blows short and swift, never two to the same place, a series of fast blows designed to keep Vader off-balance, pushing for the error. His momentum too great to halt, Vader stumbled down--
Luke lunged forward, saber before him as Vader twisted desperately to the side, his lightsaber digging a hissing gouge from the marble floor, too low to bring into play even in a hasty defense. The incoming blade brushed against Vader's leather-clad arm cutting a long slit through his heavy cloak as he rolled free, kicking out against his opponent's feet. The hurried kick caught Luke's right ankle, forcing him to stagger backwards as his weakened leg crumpled beneath him momentarily.
Vader was already lurching up again, saber before him to tap lightly at Luke's own as each regained their composure. Luke knocked Vader's lightsaber away angrily but without any real force as each circled, freshly wary, realization of the other's abilities clarified.
Over the hissing thrum of the blades, Palpatine clapped appreciatively, voicing delighted encouragement to the combatants, as if this were simply a game, a harmless distraction for his amusement.
Realization brought Vader a burst of clarity--that he was doing the very thing that he'd come here to deny. This fight could only serve Palpatine's ends; he was giving Luke what he wanted, carefully managed to better isolate and therefore control him, underlining the limits of the stormy relationship between Vader and his son.
"He wants this--" Vader said, his voice low to disguise his words. "He needs this--to break us apart. Together we're a threat and he knows it."
"Together!?" the boy hissed, tone deriding.
"He's using you--he will always use you."
"And you're so very different," Luke accused knowingly, his words a knife-twist in Vader's dim conscience.
The emotion when he spoke, the betrayal, the anger, was deeply disquieting...and distantly familiar. For Vader, seeing his son like this, the blind accusation in his face a mirror of Anakin Skywalker's on Mustafar, as wild and lost as he had ever been, everything--everything--was twisting away from him.
Luke's blade swept in again, sharp as his accusations, fast as thought, forcing Vader into defense as he realized more and more the deadly skill of his opponent. Frustration welled up at his inability to control this--to control Luke--and resentment followed it, burning away that burst of conscience in a flare of fury and firing a new purpose which pushed all other considerations aside.
The boy was committed to this duel, that much was clear--which meant that Vader must be the same.
He must bring his opponent down, as he had before. But decisively; this was no longer the same awkward, unpolished youth that he'd fought over Bespin. He needed to use enough force to stop him despite his determination... Injury was unavoidable now.
In that moment of Dark clarity, the battle between father and son became a duel between Sith.
And it could only escalate. They were past the point of no return--both combatants could not walk from this battle.
Finally accepting that this was no manageable threat, no controllable situation, Vader stepped into Luke's next assault of a very different mindset, slashing a fierce and formidable slice with vicious intent for his opponent's midsection. With hair's-breadth timing Luke intercepted the attack, but the backstep put his weight on his injured leg forcing two quick steps to that side, the power robbed from his swift parry.
Vader used his opponent's unwilling sidesteps to swing out again into Luke's path, pushing home the attack to force a slight retreat from his son, genuine anger sparking in Luke's eyes.
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.
Palpatine laughed coldly to no one but himself, the sound lost beneath the angry clash of the blades.
Vader's fighting style, his whole temperament, had escalated in the last few minutes, with Skywalker's own reaction spiraling in response. Long months of strict training were now paying off, Palpatine's harsh lessons and relentless, faultfinding criticism forcing the boy to master every weakness, oppressive discipline drilling knowledge and expertise into him, driving him to obsessively remove every defect in technique.
His fine blade. Unique and exquisite, ruthless and deadly. A flawless work of art.
.
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Luke moved without hesitation, without doubt, without anxiety. He knew that Vader was right; his real weaknesses were the injuries he had sustained at his Master's hand and his exhaustion from months of relentless pressure, never time to fully heal, to recover physically or mentally since he'd first been brought here. But all that frustration and bitter resentment could be channeled and twisted to serve now; to give power to aching muscles and failing repairs.
He wasn't afraid--death was easy, now. He'd stood so often at the brink in the past months that it held no threat anymore. But he wouldn't die without taking the source of all his torment with him.
He closed in, mind set on that end goal and what would take him there, his attack herding Vader back towards the cavernous main hall.
.
.
Beneath a hail of swift blows, Vader backstepped towards the tall double doors. Momentarily he thought this was coincidence, but the blows were too specific, his every attempt to sidestep them pointedly curtailed.
Luke was trying to back him out into the larger space of the Vermilion Hall, taking the fight to better ground, more suited to his strengths. He'd isolated his father's fighting style, his strengths and weaknesses. Now he was attempting to take control. In this confined room he'd been uncomfortably close, with no real space to maneuver in counter to his father's raw power. Speed and agility gave little advantage in a cramped space, so close that Vader had repeatedly been able to force physical contact, knowing that Luke had no defense against his tremendous physical strength. Not surprisingly, he was pushing to take the fight to a larger arena where he could better maneuver to bring his dexterity and fast pace into play.