Siren’s Lament - Part One
Yandere Siren!Illumi x Human!Reader
Summary: In a drowned world ruled by sirens, Illumi Zoldyck discovers the last surviving human in a sunken ship and slowly convinces himself she was never meant to belong to anyone but him.
Notes: this one’s going to be a long one. check my ao3! @krystalisedsoul on there too <3
Word Count: 2686
The water is black this far down, thick and endless, pressing from all sides like a thought too vast to hold. It swallows the light and hums with old voices, the kind that never learned how to fade. Illumi moves through the darkness as if he were born from it.
His body glides without effort, the faint shimmer of scales tracing his path like the memory of a blade. Fins whisper against the current, his hair drifting behind him in slow, weightless ribbons. Every movement is deliberate, a study in stillness interrupted only by the faint pulse of the ocean echoing through his body.
He is hunting, though hunger has long since stopped feeling urgent. It is simply a habit. It’s something instinctual and quiet.
There is little left in the deep worth chasing. Most creatures that wander these depths are small and half-mad from the pressure. The leviathans that remain are dull and predictable in their movements. They fill the body but not the mind.
For Illumi, the act of killing has become more ritual than necessity. He hunts because the sea expects him to, because his blood remembers that it should. The satisfaction is fleeting, the silence afterwards absolute.
Yet even that monotony shifts when he senses something strange below. It's an unfamiliar resonance that does not belong to the ocean. It smells faintly of rust, salt, and something sweet, fragile, almost floral. It feels alive.
He follows the scent through a forest of collapsed metal and coral until he finds it: a shipwreck, old enough to be part of the seabed itself. Its hull lies cracked open against a ridge, covered in barnacles and white coral growth that glows faintly under the dim bioluminescent haze. The letters along its side are long gone, its name devoured by the sea.
Illumi circles the wreck twice before entering, moving like a shadow through the shattered ribs of the ship. The silence here feels thicker than outside, the silence waiting for something to break it. He glides past broken furniture, rusted steel, and glass that drifts like frozen breath. Everything about it hums with age, and Illumi feels something stir beneath the surface of his composure for the first time in a very long while. He recognises this shape of ruin. It is human.
Humans have been gone for thirty thousand years. His mother told him their history the way other families might tell bedtime stories. The Zoldycks sang entire continents into the sea, driving humankind from the land until the last of them drowned beneath their own cities. It was an era of cleansing, she said, a necessary act of balance.
Humans were fragile but proud; they built lights that rivalled stars and thought themselves untouchable until the ocean took them. Illumi has never seen one, only the relics - broken machines, crumbling temples, bones bleached white by salt. He never cared to imagine what they might have looked like alive.
Now, in the belly of this sunken corpse of a ship, he finds something wrapped in white.
At first, he mistakes it for a remnant of the wreck. It’s a bundle of decayed cloth caught in a current. But as he moves closer, his eyes adjust to the dimness and he sees the slow rise and fall beneath the fabric. A shape, small and delicate, suspended in the last pocket of air. For a long moment, he does not move. The water around him seems to hold its breath.
He studies the figure with the same dispassionate focus he would give a strange creature he intends to dissect, but when he senses the faint vibration of a heartbeat, something inside him stills.
Alive.
The word echoes in him like a current. It doesn’t make sense. It shouldn’t be possible. The ocean swallowed every last trace of human life thousands of years ago. He knows this as the truth because his family made it so.
Yet here one lies, wrapped in a decaying blanket, breathing the ghost of air through half-parted lips. She is impossibly still, the thin lines of her body outlined by the fractured light filtering through the wreck’s broken walls. Her hair drifts across her face in threads of shadow. She is colourless and utterly defenceless.
He should kill her. That is the first and simplest answer. The instinct flares naturally, like a muscle memory; snuff out the anomaly, silence the unknown. The old song in his blood urges him to end it yet his hand doesn’t move.
He only watches. The faint trembling of her fingers in the water, the fragile pulse beneath translucent skin, the quiet rhythm of a chest that should not be rising. The longer he looks, the more the space between reason and impulse erodes. There’s no logic to the thing that coils slowly in his chest, that low hum that feels dangerously close to recognition. It is not mercy. It is not a curiosity.
He blinks once, as if the thought might dissolve with movement, but it doesn’t. It lingers, spreading through him like warmth in a body that has forgotten how to feel. The air pocket above trembles faintly as she exhales. The bubbles rise and brush against his face, warm even through the cold.
He reaches for her, and his hand closes around her wrist. The bones shift beneath his grip. She’s too soft and too fragile. He can feel the pulse flutter weakly against his palm; uneven, human. It sends a ripple through him that he does not understand. Her skin is cold, and yet somehow it feels like heat.
He studies her face closely now, drawn toward it despite himself. There’s no awareness in her eyes, only the faint flicker of life. She’s caught between the edge of drowning and waking, her body half-asleep in the water’s hold. The sight of her feels unreal and almost sacred in its impossibility. He wonders if this is what his ancestors felt before they learned how to kill without hesitation.
He knows he should destroy her; his mother’s voice in his memory reminds him of what happens to things that defy extinction. But when he imagines it, the image feels wrong, incomplete, as if some small part of him would break with it.
He gathers her carefully, almost reverently. Her head falls against his shoulder, the movement weightless and slow. The sound of her breathing is barely there, but he hears it as clearly as if it were echoing in his own chest. For a moment he stands motionless, holding her and listening to that fragile rhythm, and in that silence, something inside him begins to rearrange itself.
The wreck creaks behind him, the last breath of a dying structure. Illumi turns away, drawing her against him more firmly, his fingers pressed to the nape of her neck as though anchoring her to him will keep her from dissolving into the sea.
When he leaves the ship, the darkness seems to bend with him. The light above is faint, shifting like smoke through layers of water, and it pulls him upward. The weight of the ocean feels different now, heavier and yet strangely alive.
He does not question why he is bringing her with him or what he will do when he surfaces. Those thoughts belong to a part of him that has gone quiet. All that remains is the steady rhythm of her pulse against his skin, the proof that something impossible has survived, and the quiet certainty forming at the edges of his mind that she belongs to him simply because he found her first.
The ascent is slow. The pressure changes against his skin in waves, whispering of depth and distance, reminding him how far below the world he has lived for centuries. Illumi’s movements are effortless but careful. The body in his arms is too soft to withstand the ocean’s indifference. Every current feels like a threat, every brush of movement like a risk of breaking something that isn’t meant to exist anymore.
She drifts against him, limp and pale, her hair fanning in ribbons that shimmer faintly when the weak light touches them. The blanket clings to her like seaweed. He keeps her close, almost possessively, though he tells himself it is practicality and he doesn’t want to lose the specimen to the tide.
When he breaks the surface, the world is dim and endless. The sky is a sheet of dull grey, heavy with mist that merges seamlessly into the horizon. There are no stars or a moon, no birds. The air smells of iron and salt, and the faint hiss of distant waves echoes like static across an empty sea. Once, there were lands here, mountains and cities. Now there are only fragments of islands scattered like teeth.
He can see the outline of one far to the east, sharp against the fog. That is home, though the word feels abstract, more ritual than comfort. The Zoldyck territory. It’s what remains of an island chain carved into stone by their ancestors. His family dwells there, in caverns lined with luminous coral, their palaces sinking deeper each century as the land continues to drown.
He doesn’t turn toward it. Not yet.
The surface feels fragile, like a skin stretched thin over something much older. He floats for a while, listening. The air trembles faintly with sound, the constant hum of the deep.
Even above water, the ocean speaks in low frequencies, the song of sirens vibrating through the bones of the world. Somewhere below, he can feel the distant awareness of others of his kind, a collective pulse of voices drifting across the currents.
If they were close enough to sense what he carries, they would come. They would ask questions. They would take her from him before he had the chance to understand what she is. He lowers his gaze to her face.
The light here is weak but enough to see the fine details: the curve of her mouth, the faint tremor in her eyelids as her body struggles to adjust to the air. She’s breathing, shallow but steady. Her heartbeat is slow, uneven. The sight feels unnatural in the open sea, this fragile creature meant for another world is still clinging to life in his arms.
Humans were not built for water. They belonged to the land that no longer exists. He wonders what it would be like for her to wake here, surrounded by an endless horizon, no sky bright enough to promise survival. Would she scream? Would she understand what he is?
The thought lingers longer than it should. He doesn’t remember the last time he cared to wonder about another being’s reaction.
He begins to swim again, slow strokes carrying them across the quiet surface. The water parts easily for him, shimmering faintly where his tail moves beneath it. In the dim light, it appears almost black with hints of blue-green iridescence, long and sharp-edged. The fins that fan from his back shift and fold like thin veils.
His kind were made to be beautiful in ways that frightened prey. Their symmetry is too precise, their movements too graceful to seem natural.
Even among them, Illumi is known for the stillness that never cracks. His brothers are restless, volatile, and expressive in ways he has never been. His mother says that his quiet is the sign of a perfect predator. Although now, he feels the silence pressing too heavily around him.
He glances at her again, studying the way her fingers twitch slightly when a drop of water touches them. The motion is small, involuntary, but it captures his attention completely. There is something about human fragility that unsettles him. Everything about her seems unfinished. He’s unsure if it’s because her skin is so thin it shows veins beneath, her breath shaky and uncertain or because her bones felt delicate enough to shatter under his hand.
But somehow, across thousands of years and the ruin of her species, she still exists. It feels wrong but it feels important.
He thinks of his mother’s voice, melodic even without singing, teaching him as a child about the order of life. Sirens consume what is weaker. The sea consumes what is careless. There is no cruelty in it, only necessity. To spare something weaker is to disrupt the balance.
But as he holds this impossible creature, he cannot help but feel that she has already disrupted something far older than law. She does not belong to the sea, and yet the sea has kept her. Perhaps that means she belongs to him now, because he was the one who found her. He pushes the thought aside, though it continues to circle like a slow current beneath his calm.
The fog grows denser as he drifts further from the wreck. The surface light dims to a dull glow, and the air chills. The only sound is the quiet lapping of water against his shoulders. He finds a fragment of rock jutting above the waves, a piece of drowned land, nothing more than a jagged ridge slick with moss and barnacles. It will serve.
He hoists her gently onto it, the movement careful but firm, arranging her so her head rests where the stone dips shallowly into water. She doesn’t wake. The blanket clings to her body, soaked through but still somehow bright against the grey.
He studies her in silence. The air here is too thin for him. He rarely surfaces for long, the weight of the open sky pressing on him like a threat. He feels exposed, unnatural. Still, he doesn’t return below. He kneels half-submerged beside her, watching the slow rhythm of her breathing. His thoughts shift between logic and something older, harder to name.
There’s no reason to keep her alive; she cannot survive long in this world, and he cannot take her among his family without consequence. His mother would want her voice tested, her mind picked apart, her body kept as an ornament. His brothers would mock his hesitation or try to claim her themselves. He can almost hear their voices in his head already. The curiousity, the cruelty.
No, she cannot go to them. Not yet. He needs to understand what she is first. Perhaps she isn’t entirely human. Perhaps some fragment of siren blood kept her alive. Perhaps she is something new. These are rational explanations, but none of them feels true.
He leans closer until he can hear her heartbeat again. The sound is small but clear, a fragile percussion against the quiet sea. He realises, distantly, that he likes the way it sounds. It is inconsistent and unpredictable.
Every siren heartbeat is perfectly timed, a rhythm that never falters. Hers stumbles, catches, resumes. It feels alive in a way his kind no longer does. The thought should disturb him. Instead, it steadies something inside him that he didn’t know was shaking.
Illumi straightens slowly, his gaze never leaving her face. The mist gathers around them like gauze, the sea rolling gently beneath. Somewhere far below, the songs of his kin continue to hum through the water, but none reach this high. For now, this place belongs to him alone. He does not know how long he will stay here before the pull of home becomes impossible to ignore. He only knows that he will not leave her. At least not now.
He lowers one hand back into the water, feeling the vibration of the deep return through his skin. The ocean wants her back, but he will not give her to it. The logic of the world has always bent for his family’s will, and he does not see why this should be different. If the sea has chosen to preserve her, then perhaps it did so for him.
The thought comforts him enough to quiet the unease. He lets the water ripple against his hand, the motion almost tender, and watches the faint rise and fall of her chest. In that fragile rhythm, he imagines the beginning of a new kind of silence. One that belongs only to him.
