Uchiha Shisui and the Naruto universe are the creation of Masashi Kishimoto.
Author's Note: In Chinese astrology, Mars is ruled by the element fire. It is also the Roman god of war and bloodshed. Both the soil on Mars and the hemoglobin in blood are rich with iron, which gives them their distinct red pigmentation.
Shisui never wanted to be a shinobi. He spent his formative years chasing shuriken and perfecting katas because that is what young Uchiha clansmen did. And if Shisui ever really wanted to be anything, it was an Uchiha. He wore the clan crest like a badge upon his heart and a sign upon his wrist, an indelible reminder of where he came from and who he would become. Birthright was a misnomer in the clan - you had to earn the name Uchiha. So Shisui bent and beat his body like the malleable iron of a katana, waiting for the day he would be made like steel in the sacred flames of the Uchiha namesake.
When Shisui was eight years old he activated the Sharingan. It was an accident, really. He hadn't wanted to kill the big man from Stone, but his father and his uncle had been gone for three whole weeks when the village was attacked and Shisui had promised them that he would be a good little soldier and protect his aunt and baby cousin while they were away being real shinobi. The Stone ninja had mean eyes that glinted maniacally as he made craters in the ground with his fists, great cracks that swallowed whole his aunt's tidy flowerbeds and rattled tiles loose from the roof to fall to earth like broken stars. And before Shisui knew what he was doing the world had shook itself into shocking clarity and he was vaulting upwards to drive a kunai through the flesh and muscle of the big man's throat, because even if he couldn't spell 'jugular' he still knew it bled liquid life. Warm blood, a brilliant candy red, spurted across his shirt and face before Shisui remembered to keep moving, the body crumpling bonelessly beneath him. And then his aunt was screaming his name and dragging him away from the dead man and shaking him by the wrist, telling him to turn it off - turn it off, goddammit! - until his chakra lashed violently back on him like his father's fire whip. It was only then, after his peripheral vision snapped shut, that Shisui realized he wasn't breathing and stopped to swallow air before vomiting spectacularly all over his shoes.
They told his father afterwards, when Uchiha Hiroto came home broken and burned and forever without the use of his legs, that Shisui was one of the youngest in clan history to awaken the Mirror Wheel Eye. His father regarded him silently from his hospital bed, the weight of his unfathomable gaze settling like a lead mantle on Shisui's shoulders.
The cutting began when he was eighteen. He'd sit on the edge of the bathtub, the porcelain cool against the back of his thighs, and methodically roll up the cotton sleeve of his left arm. In the harsh fluorescence of the bathroom, the smooth skin of his forearm always looked unnaturally white...which only made the blood that much brighter, thick beads of velvet crimson that budded forth from the pattern of thin red stripes he traced with the edge of a razor, because kunai were too sharp.
It was comforting to know that despite everything, he still knew how to bleed.
Afterwards, he'd rinse the blood from his arms, watch the water disappear down the drain, dragging swirling ribbons of pink behind it.
On his twelfth birthday, as they waited for death in the northern trenches and the conflict on the border raged its way to a bloody close, Shisui's commanding officer promoted him to chunin. It was a token commendation, done solely to balance the numbers and make it appear to the angry villagers back home that one less genin was forced to die in battle. Not that Shisui didn't deserve the promotion - it had been over four years since he first tied on his hitai-ate, and there was a reason he was serving on the front lines rather than running messenger duty or performing some other equally mundane task. Shunshin no Shisui, they called him. The speed of his Body-Flicker technique, combined with the precision of his nascent Sharingan, quickly gained battlefield fame among Stone and Leaf ninja alike.
An explosion sparked a half-mile down the front, raining pumice from the sky and rocking the ground beneath Shisui's knees as he crawled belly-down through the muck and mud to lap from a stagnant pool of rainwater. There was grit under his fingernails and blood and other equally unpleasant things splattered across his vest, most of it not his own. As far as Shisui knew, he was born to die here. The war was a dictate that tithed his childhood and cast him into the gladiator's ring to fight the lions without spear or shield. He did his best to remember what his teachers and his sensei had told him, to fight not only bravely but intelligently and efficiently as well. Sometimes he'd think back to the first man he ever killed, and wonder at how strange it was then to watch and feel a person's life leave their body and drip like thick paint from his fingertips. Now it was almost too easy to flit like a swallow behind an enemy's back, crimson eyes spinning lazily, and drive a kunai beneath armor into the soft tissue of a kidney. A comfortable rhythm where he moved and didn't think and let the battle adrenaline take him to some sick, red-tinged parody of elysium.
But currently they'd been in this stinking pit for a week without food or water or prospect of escape. Shisui counted his remaining weapons (three shuriken, two kunai, one explosive tag) like he counted his remaining days. He tried hard not to think of his Aunt Mikoto, the closest thing he ever had to a mother, swollen with child and bending lovingly over her rosebushes. Or the way Itachi had, with solemn eyes, refused to cry as Shisui bid him goodbye. What he did think of were the hard planes of his father's handsome face as he knelt obediently in front of Hiroto's wheelchair. Their parting words were a mandate, a banner to carry into battle, more binding than any jounin commander's: honor the Uchiha. Now, in the gathering dust and debris of battle, Shisui could do nothing more than pray that when they brought his dogtags home, his father would understand he'd tried his best.
"He's just a child!"
"In the eyes of the clan he's not."
"Damn the clan! I promised my sister when she died that I'd watch after him -"
"And you have Mikoto. But he's Uchiha, and a boy becomes a man the day his Sharingan is born."
"So you would willingly send him to his death? What if it were Itachi in his place? What if it were you're own son?"
A beat. A breath.
"I'd send them both. It's my obligation. It's their obligation."
On a moonless night, a month after he awoke the Sharingan, Shisui's uncle came to collect him. He took him to the clan shrine above the river and lifted the seventh tatami mat from the east wall to reveal a secret underground chamber. Hesitantly, Shisui clambered downward into the inky darkness. It seemed as if the entire clan was gathered in this secret room, pressed shoulder to shoulder and watching him with red-lit eyes. The scattered pinpoints of candles cast flickering shadows that swayed eerily along the bare stone walls. Fugaku led Shisui to the front of the room, where the clan elders stood in front of a polished bronze altar. An ancient looking scroll hung behind them, written in a language Shisui did not recognize.
"Kneel," the elders intoned, and with stiff knees Shisui obeyed, his small shoulders shivering with cold and not a little fear. The air in the room was thick with a strange energy, almost oppressive - the combined chakra of a powerful and dangerous clan that had risen to the forefront of Konoha's elite.
"You are here tonight, Uchiha Shisui, to bear witness to the ancient traditions that bind our sacred brotherhood. Do you, as the next successor to the Sharingan, swear your loyalty to the Uchiha and promise to honor the mystic secrets and ideals of its heritage?"
Shisui, young as he was, knew that it would be sacriligeous not to answer. From their earliest comprehension, every son of the Uchiha learned through sacred story and song that the acquisition and mastery of the Sharingan was the greatest achievement a clansman could make, and yet the Sharingan did not deign to gift everyone. Shisui had been chosen; he could not refuse his destiny. So he said yes, and did not flinch as his uncle drew a kunai across the tender flesh of a forefinger to squeeze a single drop of blood onto the parchment laid upon the altar, a symbol of his eternal commitment to the clan. And then, in a knarled baritone, the elders commanded him to rise and activate the Mirror Wheel, and as his fledgling Sharingan materialized, chakra creeping outwards to mingle with that of the entire clan, the aged scroll on the wall shimmered with the secrets and the bloody history of the Uchiha. Shisui read the elegant characters silently, a gateway to his past and his future, and realized with dawning horror that some traditions were better left unremembered.
The Sharingan is a map that leads to nowhere, Shisui thinks. He's lounging on the roof of the clan meeting hall, head pillowed on one arm, staring at the glittering swath of constellations that spreads above him. The stars are particularly bright tonight. When he was very small and full of a child's eager, darting enthusiasm, he'd dare himself to break the speed of light, to move so fast even the stars couldn't keep pace. He reflects now, a lifetime later, that maybe some barriers aren't meant to be broken.
Shisui pretends not to notice the soft footfalls that approach him from behind, nor the quiet flicker of Itachi's chakra as the younger boy settles down next to him. Itachi tilts his head back to bask in starlight, a fringe of lashes casting feather-stroke shadows across sharp cheekbones. The silence is pregnant with all their hollow thoughts, a rash of dew-drop words that collect in the back of Shisui's throat. He swallows involuntarily before lifting a finger to point at one particularly bright, red-tinged star rising in the east.
"You know the name of that star, 'tachi?"
Itachi breathes in the familiar nickname and regards the star with one heavy-lidded glance. "Mars," he responds with his customary placidness.
"Mars," Shisui echoes. "Our ancestors once worshipped Mars as the astrological sign of the Uchiha. Did you know that?" He chuckles briefly and softly. " 's fitting, I think."
"Shisui..." Itachi's tone is low, warning. He turns his head to look at his cousin, but Shisui just keeps studying the sky and doesn't meet his gaze. There's a bitter kind of sadness lurking behind his onyx eyes and turning down the corners of his mouth. "It doesn't have to be like this. We could speak to the elders, try and persuade them otherwise -"
"No, Itachi." Shisui's voice is hard and brittle like flint. He swings his head around to lock eyes with Itachi, and Itachi can see the shadow of a millenia of war and bloodshed in Shisui's face, cold resignation and something almost desperately earnest drawn in the centurial line of his mouth and the handsome slope of his forehead. "It's too late for that," he whispers, lips curving wistfully, and the gesture is so heartbreakingly beautiful it makes Itachi ache.
Shisui's expression softens as he regards his younger cousin, more a brother than their blood denotes. Although five years his junior, the boy is his equal in every way possible, save one: he's still worth saving, young enough and unblemished enough to requite his sins and the sins of his clan. Someday, when all is finished and the name of the Uchiha is nothing more than a bad honorific in the annals of Konoha history, Itachi will be remembered - no, honored - for choosing country over kin. Shisui knew, that dark night years before when he signed his life away in blood for an ideal he never really believed in, that it was too late for him. But he would make sure, with his dying breath, that it wasn't too late for someone else.
The depth of duty stretches between them while the heavens make their slow revolution. Shisui leans back and contemplates the nature of redemption.