A sadistic Princess should have a sadistic knight.

Flowers.

(A/N: slight gore. You have been warned.)
Kamui drank in the metallic smell of blood. He descended down the corridor, his hands and umbrella drenched in crimson. Butlers, maids, and guards lie motionlessly in their own pools of red; the pulchritudinous flowers that formed on the ground with every shot of his umbrella and strike of his limbs filled him with an ominous tranquility.
"Damn monster," Takasugi muttered beneath his breath, impaling the man beside him without breaking eye contact with Kamui's back.
This implacable massacre was executed with nightmarish speed. So quickly one could end a life, and so quickly one could end ones own.
     "Takasugi-chan, watch out~" Two fresh katanas impeded his path as Kamui receded down the hall, anguished screams reverberating off the marble walls.
     "That's enough, you demon," Gintoki said acidly. His teeth were clenched, and his eyes were watery with tears. "You killed my family."
Takasugi glanced at the elderly man with several gun wounds to his head, the young, freckled boy with greenish hair who laid on his back, a gash going diagonally across his abdomen.
     Katsura tucked his white penguin puppet into his pocket and his long, inky hair was tied up in a high ponytail. "Therefore we will kill you today."
...
Tsukuyo launched kunai at Henpeita. He deflected them with ease, emotionless and horribly irritating.
"Watch yer back, ugly!" Matako exclaimed, aiming her gun at her back.
"Watch your back," Kyuubei scowled, thrusting the hilt of her katana into Matako's spine. She cursed and swivelled around. Otae kneed her in the stomach, her eyes widened.
Sarutobi emerged from the shadows, Zenzo following suit. "We're going to punish you for trespassing."
...
Kamui rounded the corner, snapping a soldier's elbow and whisking the severed arm into three other men, causing them to fly backward. He fired bullets and one by one, shot them down.
They're like cockroaches. They keep on coming even if they know they'll die if they do.
"That's enough."
Slowly, suspensefully, his gaze travelled upwards. Standing before him was Kagura. Poised, sobbing, and furious. He grinned, and to his upmost pleasure she looked frightened. He punched her. But she didn't budge. With a grip that made him stand transfixed by her strength, she forced him backward.
"Well," he chuckled, rocking his wrist to ease the pain, "well, well, well."
Unsurprisingly, Sougo and Hijikata ran in.
"Hime, leave, we'll take care of this!" Sougo demanded, shocked she managed to arrive to the battlefield before them.
She turned to him. "No." And she steadied her eyes on Kamui once more. "Now, I thought I didn't have any siblings. But then I heard your voice. How nostalgic. How frank and unambiguous your words were, Onii-chan."
Kamui chortled. "I'm overjoyed you regained your members, Imouto-chan!" He licked his lips and looked past her. "But unfortunately, I have to end your lives." She was struck with waves of fear. He was referring to Sougo and Hijikata.
"That works vice-versa," Hijikata retaliated coolly.
"I hope you know that," Sougo added, "you will not leave this castle alive. I," he tightened his fist about his signature golden hilt until he shook with anger, "will torture you. Make you feel the worst pain in the world. And I'll do it with a smile."
Kamui pursed his lips distastefully, and kicked a soldier to the wall.
"I don't know why you are so disturbed by this. I only decorated the place, festooned it, what more could you want than lovely red flowers? Don't you want to be flowers too?" He said this with an innocuous shrug before hurling himself at them.
...
Bansai ran through the profusion of flowers; thornless roses, chrysanthemums, sunflowers, daisies, he ripped them out of the ground with every kick-off.
"Alright, let's not ruin the garden."
He stilled and prepared himself. He was profoundly unfazed by Kondo's menacing entrance.
Disheartened, Kondo unsheathed his sword and allowed it to glint and reflect in the sunlight, which wasn't thematic at all being that precious lives were lost. He inhaled a drastic amount and yelled: "YAMAZAKI, OTOSE, SAITOU, THIS IS FOR YOU!"
He sliced Bansai's leg, and he in return marred his cheek. They grit their teeth.
...
Tsukuyo pinned Henpeita to a wall and sent a barrage of kunai his way. Too exhausted and injured to dodge them, he stood there, oscillating as the sharp needles pinned him to the veneer walls of their grand hall.
"That's one."
Kyuubei and Sarutobi, very close to unscathed, brought Matako over and tied her to a pillar.
     "Let's get everyone out. Evacuate quickly!"
...
Sougo charged into Kamui, but he briskly avoided the attack, thrusting his knee into the knight's stomach. He cried out in pain. Kagura shot at his head in a relentless barrage of bullets, but to no avail; Kamui was unharmed. At this point, they were nearing unconsciousness. Hijikata forced himself upward and ran forward, even though his legs were splitting and his mind was whirling and he didn't do much to scar the intruder. Kamui snapped his umbrella emphatically onto his head and he collapsed and sprawled onto the floor.
"Ngh.."
Something grabbed onto his elbow.
"Seriously, Hijibaka, I know I joked about killing you, but it'd be kind of troublesome if you died right now."
He was propped up against the wall and he felt a dramatic loss of self-gratification.
...
Gintoki stabilized himself on Katsura's shoulder and he in return grasped his wrists tightly and swung him into Takasugi, who avoided the unprecedented attack by a hair. They were badly injured, and their clothing merely consisted of mangled silk and cloth. All three men were breathing heavily, but showed no indication of giving up.
"Hey, Taka-" a clash, "-sugi, why are you even here?"
Katsura lacerated Takasugi's side and he let out a strangled, chilling laugh and used both his sheath and his blade to force them backward with some immense strength he supposedly kept dormant for moments such as this. They staggered as he flew towards them. They leapt back, poised for action.
"You're asking that now?" He inquired, slamming his weapon onto them, causing them to use a reflexive parry.
"Gintoki-" clatter. "On three."
Takasugi grinned, hopped on his hand and sprung farther away. His pupils were dilated, and his katana was wedged between pearly rows of carnivorous teeth. An abnormally smile was on his lips.
Katsura and Gintoki were silent for a moment, then scoffed at one another. "We've seen scarier."
...
"Wipe that creepy-ass smile off your face, you beast," Sougo said angrily, slipping his blade into Kamui's abdomen. Kagura followed with a resounding kick to his head. Splatters of blood flowed from his nose and stomach. But his flexed mouth muscles never gave way, occasionally paused to moisten stained lips.
Kagura smiled as well and kneed him ferociously in the back. He was rushed across the hall and was crushed against the wall, stones and other debris crumbling as he tore his severely injured body from the rummage; that smile never once wavering.
Sougo whistled and turned to her. He was shocked to see a widening, maniacal grin plastered on her face. Splotches of crimson marked her porcelain skin, and she licked it away.
"Good kami. Like brother like sister indeed," he said, disturbed.
She dropped it and pulled him along, her trademark, Kagura grin displaying itself on her features as she reached for his hand. "Hurry, Sadist. Isn't this fun? How long has it been?"
Sougo immediately shoved her to the side as Kamui accelerated into the wall just millimetres away from their faces. He successfully drilled a hole into the wood. Kagura retaliated with a bullet to his leg. He clenched his teeth and clutched her head with a grip like adamantine. She had no fear in her eyes. He was struck with horror.
Then he released. And dropped to the floor.
...
Bansai and Takasugi exited the castle wordlessly, supporting Matako, Henpeita, and Kamui on their shoulders. They limped to their boat and sailed away, in permanent disbelief with the results of their attack.
     Kamui blinked and shot up violently, looking around wildly. "Imouto-chan? Kagura?"
     "Don't bother looking for her," Takasugi said nonchalantly, firing his pipe and exhaling heavily. "She's not here. Your plan was absolutely idiotic. You better make up for it."
     Kamui shrugged and chuckled. "Maybe we should plan an infiltration later on."