The Sound Between Heartbeats: An Original / FF 7 Crossover Fic
Summary: During a Shinra lockdown, Sephiroth confronts a howling abomination born of Project N while shielding Bianca.
Pairing: Bianca Moore (f!oc) / Sephiroth
Other Characters: Angeal Hewley (mentioned), Hojo (mentioned), SOLDIER units (mentioned), Project N Creature
Possible Trigger Warnings: body horror, chemical/industrial smells, death, graphic violence/gore, human experimentation/vivisection, loud noises/sonic/psychic assault, medical experimentation/non-consensual procedures, monster/creature violence, nausea/illness depiction, references to trauma, miscarriage (mentioned)
Possible Tropes: Action sequence, Body horror, Containment breach, Creature attack, Hurt/comfort, Laboratory / mad scientist, Medical experimentation, Protective partner, Red String of Fate / soulbond, Sonic/psychic assault, Violence/gore, sane!Sephiroth, pre-fall Sephiroth
Author’s Note: This piece was created for @flufftober, Alt 12 (keeping someone safe) and alt 20 (I got you), It is also for Sephiroth Week hosted by @week-of-silver-winds, prompt: Day 7 (Howl).
This is the final day of Sephiroth Week. I was so excited to participate in it again this year.
The Shinra Building slept uneasily.
Metal groaned somewhere above, the sound carrying down seventy floors of glass and steel like the breath of a restless beast. A low hum threaded through the air: the steady thrum of mako conduits deep within the walls, alive and pulsing, a heartbeat for the empire that fed upon it. Sephiroth stood in the dim corridor of the executive wing, as he always did. His silhouette tall against the faint green glow that seeped through the vents.
The building was on lockdown. Red warning lights burned intermittently along the walls, flickering like slow, uncertain flames.
Somewhere beyond, alarms muttered in soft tones: restrained, almost polite. The intruder was still contained in the lower levels, yet the tension in the air coiled tight, like the instant before lightning strikes.
His hand wrapped around the hilt of the Masamune. The steel was cold, yet comforting; a promise of control amid chaos. He listened. His breath slow as he closed his eyes for a moment.
The vibrations in the floor, the subtle flicker in the power grid, even the change in the air pressure. All of it spoke to him. But beneath those physical currents was another, more intimate pulse: the Red String of Fate.
It tugged warmly and faintly against his wrist. Its presence was something that he grew familiar with long ago, as it had always been there.
Bianca.
Her presence shimmered against the edge of his awareness like candlelight through fog. Her emotions were muted but tangible: fatigue, discomfort, and the steady rhythm of her breath strained by something unspoken. The tug deepened: a whisper that felt less like pain and more like the body’s plea for gentleness.
He frowned slightly.
She was strong: stronger than any humans and many gods. Yet through their bond, something fragile pressed through tonight. The Red Thread pulsed once, tightening, and Sephiroth turned sharply. His long coat whispered behind him as he moved and searched for his wayward wife. They had married the previous week in a ceremony that was for Shinra and not themselves.
He found her two corridors down, in one of the narrow auxiliary passageways used by high-ranking SOLDIERs. The lights here flickered faintly, as green merging with sterile white.
Bianca stood braced against the wall, one hand resting just below her ribs, and her other pressed to the cool metal panel beside her.
Her wings folded close and shivered faintly with each breath.
She wore her crimson turtleneck, the Shinra insignia glinting faintly beneath the harsh lights, her brown suspenders strapped horizontally across her torso. She did not wear them like he did, crossed over his chest.
Her skirt brushed her thighs with each slow movement, and the black leather of her boots gleamed faintly with reflected emergency light. Strands of her dark hair had escaped their ribbon, curling damply against her cheek.
When she looked up, her indigo eyes met his. Her pupils narrowed to slits, as he stood there: tall and imposing amidst the pulsing green light.
“I’ll be fine,” she murmured softly, her voice steady but tired. “Just . . .tired.”
Sephiroth’s gaze traced her face: the pallor beneath her makeup, the faint tremor in her hand. There was a sheen of sweat at her temple. She bit her lower lip unconsciously, a nervous habit he recognized, and his chest tightened in response to it.
More than tiredness, he thought.
He stepped closer, the soles of his boots silent against the floor. “You are pale,” he observed, tone even but weighted. "Again."
She exhaled, a shaky little laugh. “Long day.”
The faintest flicker of nausea rippled through their bond, brushing against his chest like static. It wasn’t sharp enough to incapacitate her, but it was there.
Beneath it, something warmer, heavier: a subtle ache low in her body that translated through the thread as a pressure against his ribs. He masked the flicker of concern, shifting slightly to position himself between her and the end of the corridor.
The smell of disinfectant hung heavy in the air, mixing with the bitter aroma of brewed coffee wafting from an open office down the hall.
Bianca wrinkled her nose. The motion so small that most would have missed it. But Sephiroth noticed. He always noticed. Her wings twitched once, feathers rustling, and her expression pinched as though the scent itself scraped across her nerves.
“You dislike the smell,” he said quietly.
Her lips twitched. “You could say that.”
The Red Thread pulsed faintly in agreement. Warmth bloomed where it touched his skin.
A low tone interrupted them: an alert chiming in Sephiroth’s earpiece.
“Containment breach detected,” the robotic voice announced. “Specimen. Unidentified. Sector sixty-seven. All personnel to designated lockdown zones.”
Bianca’s breath hitched. The faint glow of the alarm light bled over her face, tinting her features scarlet. Sephiroth turned his head toward the direction of the alert. His mind already calculating distance and response, yet that tug from the thread persisted: a faint pulse of distress from her side.
“Stay behind me,” he said, not a command but a quiet certainty.
She arched a brow. “You know I don’t—”
“Bianca.” His tone softened just enough to silence her.
For a moment, she looked as though she might argue. Then she pressed her lips together and nodded once, shifting closer. The warmth of her aura brushed faintly against his, a quiet shimmer of celestial and infernal energies intertwined. He could feel the tremor in her frame—subtle but there—her breath quickening slightly as they moved toward the elevator access.
The freight lift to Hojo’s laboratory creaked open when Sephiroth keyed in the override. The metallic scent grew stronger as they descended, mingled with the hum of mako tanks and ozone. Bianca’s expression tightened. She pressed her knuckles briefly against her mouth as though steadying herself but concealing the small, gagging sounds she made.
When the lift stopped, a dense silence met them.
Floor 66. Hojo’s laboratory.
The lights flickered overhead, casting long, shifting shadows over the glass containment pods lining the corridor. Each held its own quiet horror: shapes that had once been animals, now suspended in pale fluid. Wires threaded through translucent skin. The smell of sterilization fluid and burnt ozone was thick enough to taste.
Bianca’s breath came shallow. “Something’s wrong,” she whispered.
Sephiroth didn’t need to be told. He could feel it. The air was alive with an unfamiliar vibration, a frequency that made the mako conduits tremble. Somewhere down the hall, a metallic crash echoed. It was followed by a low, wet growl that didn’t belong to anything human.
When it came into view, even Sephiroth paused.
The creature was a grotesque fusion of flesh and shadow: humanoid only in the vaguest outline. Its body shimmered with iridescent veins of glowing, emerald mako and something darker. Black fluid seeped from cracks in its hide and puddled onto the floor.
Multiple eyes blinked across its shoulders and back: some glowing blue, others red, each focused on a different direction. Never blinking. From its spine unfurled a pair of fetid wings. They were not feathered like Bianca's but slick with residue. Each movement accompanied by a stench like burning chemicals.
The scent hit Bianca first. She inhaled sharply. Her own wings twitched, as she almost backed away.
"Stay close," Sephiroth ordered.
"That thing,” she whispered, as her voice cracked like thunder breaking the calm. “It carries the same blood. Mine. But mixed with something else.”
The creature’s head snapped toward them, and it howled.
The sound tore through the corridor like a blade through glass: raw, metallic, resonant enough to make the mako conduits shudder and pause. The vibration crawled down Sephiroth’s spine, a low buzz blooming behind his temples.
His enhanced senses reeled under the assault. Even the Masamune’s metal hummed faintly, sympathetic to the frequency. Bianca flinched. She folded slightly. Her hand pressed to her abdomen as the howl raked through the air again. Higher, shriller, wrong.
Sephiroth caught her before she could stumble. His arm circled her waist with the ease of instinct. Her breath trembled against his chest for a heartbeat before he spoke, calmly, steady, and a still point in the chaos. “I’ve got you.”
The Red String burned faintly around his wrist, carrying the pulse of her distress through him. Then he released her with deliberate precision, stepping forward as the lights flickered overhead. His voice dropped into command-channel calm.
“All lower-ranked SOLDIER units failed containment,” he said into the comm. “I, Sephiroth, am engaging.”
The howl came again closer this time, shattering glass along the corridor. Sephiroth raised his blade, the Masamune gleaming with reflected mako light near the left side of his face and shoulder.
“Stay back,” he told Bianca. “It reacts to movement.”
Then he moved: fluid, lethal, a whisper of silver and shadow. The creature lunged. Claws dripped with black ichor. Its fetid wings battered the air. Each step it took reverberated through the metal flooring. Its eyes pulsed like dying stars. Each resembled Bianca and his eyes.
Sephiroth met it head-on.
He blurred forward in a flash of motion, striking quickly. Eight slashes fell in rapid succession. Each so fast that the very air itself seemed to tear.
The creature shrieked and howled at once. Its cry rose into a psychic pitch that sent sparks across the walls and static through Sephiroth’s mind. For a heartbeat his vision fractured. The world reduced to pulsing color, and Bianca’s aura a faint glimmer in the haze. He forced focus through sheer will, driving a booted heel into the floor to anchor himself.
“Enough.”
His palm turned upward. A circle of red materia flared at his belt. Heat rippled through the air as a fireball hovered over his palm, growing in strength and size. The fire burst forth in a precise, searing arc, engulfing the creature in a tide of molten light.
It screamed: a sound that shifted instantly back into that same, bone-shaking howl. Its flesh slouched off, blackening and charring like burnt chicken skin. The burnt stench wafted between the creature and them.
The psychic frequency slammed into him again and was sharper this time, buzzing like hornets under his skull. He gritted his teeth, pushing through the distortion. He’d endured worse in the mako chambers and Professor Hojo during training. He would not falter now.
Behind him, he felt Bianca’s aura flicker with nausea. Her breath caught audibly. He adjusted his stance instinctively to shield her from the worst of the reverberations, angling his blade to reflect the blast of heat and sound. His hair whipped around his face and against his back and shoulders, as the Masamune bent the sound around them.
The creature lurched forward. Its half-melted wings flapped weakly, and its body dripped with smoldering residue. Sephiroth moved again. Smooth and as quick as an exhale: one clean arc of motion. Silver sliced through the vibrating dark. The blade cleaved deep, meeting flesh, muscle, and bone, cutting through core and shadow alike.
Its final howl was deafening: an unholy wail that rolled through the floor and up the walls, making every glass cylinder shiver.
Bianca’s wings flared reflexively. Her feathers rattled, as her hand pressed hard to her lower ribs as if steadying herself against the invisible pressure.
Then the sound broke.
The creature collapsed in on itself. Black fluid hissed as it met the floor. The lights overhead steadied. The psychic buzz faded from Sephiroth’s mind, leaving only the quiet hum of mako and the faint rasp of Bianca’s uneven breathing behind him.
Through the Red Thread, he felt it again. Her nausea sharpened, and her pulse uneven: a illness he had felt since Angeal's Day of Remembrance a month ago.
He forced his movements to remain precise despite the awareness clawing at his focus. He ended the monster with one clean strike now. The blade tore through core. The body split with a wet, final sound before collapsing in a heap of hissing flesh.
For a long moment, the only sound was the distant hum of the mako tanks. Then the sirens dimmed. The air, though still thick with iron and ozone, began to settle, as its body started to fade out into tiny motes of green light.
Sephiroth turned.
Bianca stood against the wall. One hand pressed to her chest, and the other resting low on her abdomen. Her wings trembled faintly, feathers ruffled. Her eyes found his: dazed but aware.
“It’s over,” he said quietly, as he dismissed the Masamune. The blade slowly disappeared when purple mist moved along its form.
She nodded, but her response was delayed.
“That. . .thing. . . ” She swallowed hard, as the color drained from her cheeks. “It was part of Project N, wasn’t it? Part of us.”
He didn’t answer.
Her body swayed slightly, and before thought could intervene, he was beside her again. One arm steadied her by the shoulders. She tensed briefly, then exhaled, and leaned into the contact just enough for him to feel the minute tremor running through her frame.
“I’m fine,” she murmured again, but her voice had softened, unraveling at the edges.
“You are not,” he said simply.
Her lips parted to argue, then closed. Instead, she let him guide her away from the laboratory, through the silent hallways and up the freight lift toward the quieter executive floors.
Each level they descended seemed to leach a little of the tension from her body, though he could still feel the strain humming faintly through their connection: an ache, a fatigue that refused to fade.
When they stepped into one of the smaller rest quarters near the 59th floor, the sudden stillness enveloped them. The room was modest by Shinra’s standards: a small couch, a table, and soft light filtering through glass panels.
Outside, the city shimmered beneath a dark sky. Midgar's reactors glowed faintly with emerald light, a beacon against the night.
Bianca sank onto the couch, exhaling. Her wings folded tightly around her. The feathers dimmed to a dusky hue.
Sephiroth remained standing for a moment. After a pause that might have been hesitation, he knelt before her.
Her hands were clasped together in her lap. Her knuckles were pale. He reached out, the leather of his gloves creaked faintly as his fingers brushed her wrist. The Red Thread glowed faintly between them beneath his glove and around her flesh, warmth radiating in the space where string met skin.
“You are trembling,” he said quietly: a bit too quiet.
“I’m tired.” Her tone was soft, but something beneath it carried a note of vulnerability she rarely allowed anyone to hear. These were moments only Sephiroth witnessed.
“It’s been a long day, and my body’s just—”
She stopped, grimacing faintly as another wave of discomfort rippled through her. Her hand shifted instinctively toward her lower abdomen. “It’s nothing serious.”
Through the bond, he felt it again: not pain, exactly, but heaviness. It was a quiet, deep strain that seemed to draw energy from her very bones.
He studied her face: the faint shadows beneath her eyes, the pallor at her lips, and the way her breathing caught just slightly after each exhale. He had seen her after illnesses, after torture, but he had never seen her like this.
“You have overexerted yourself,” he said.
Bianca smiled faintly, the curve of it weary but sincere. “You sound like Zack.”
He didn’t return the smile. “Zack does not carry command authority quite like I do.”
That earned a soft chuckle from her, but it quickly faded as she leaned back, eyes closing. A lock of her black-and-indigo hair fell forward. He reached without thinking, brushing it aside with the backs of his fingers. Her scent lingered faintly in the air—something like pumpkin spice—threading with the faint chemical sweetness of mako.
Her breathing evened out gradually, but he could still sense the discomfort underneath. Through the Red String, it pressed against him like a low hum. He found himself matching her slow and delibrate rhythm, until the pulse of the thread steadied.
Minutes passed in silence. The only sound was the faint whir of the building’s systems and the occasional creak of the wind against the windows.
When she finally spoke, her voice was soft, almost drowsy. “You shouldn’t worry so much.”
“I do not,” he said automatically.
Her lips curved again, just barely. “Liar.”
He said nothing.
She opened her eyes then, and their indigo depths reflected the faint green light filtering from the city below.
“You always try to carry everything alone,” she whispered. “Even me.”
He met her gaze, expression unreadable. “You are not a burden.”
Her fingers brushed against his, the contact feather-light. “Then stop treating me like glass.”
He did not withdraw.
“You are not glass,” he said quietly, “but you are breakable.”
The words hung between them. It was just the unadorned truth. Bianca looked at him for a long time, something unreadable flickering behind her tired eyes. Then she leaned forward, resting her forehead briefly against his shoulder. It was a gesture so small, so tentative, that he might have missed it had he not felt the surge through the Red Thread: the warmth, the ache, the quiet gratitude.
His hand lifted slightly, hovering just above her back. Then he allowed it to rest there, a careful weight, steady and grounding. Her wings relaxed beneath his palm, as the feathers rustled softly.
Outside, another storm began to gather over Midgar. It seemed to rain wherever Bianca was. Distant thunder rolled across the skyline, the scent of ozone filtering in through the vents. Bianca’s breathing deepened, and her body finally loosened the last of its tension.
Sephiroth watched her in silence. Her pallor remained, and the faint sheen of exhaustion clung to her, but there was a softness in her expression now: a quiet peace that made something in his chest ease. The Red String pulsed once more. Slow and certain.
Even when she had morning sickness and weakness from their previous failed pregnancies, Sephiroth did not understand what had unsettled her body tonight. Whether it was stress, exhaustion, or something quieter and deeper blooming remained unseen. But he knew one thing. Whatever it was, he would not allow it to break her.
His gaze lingered on her profile, as the faint color returned to her cheeks and the way her lashes trembled. She drifted near sleep. For a moment, the chaos of Shinra and the horrors of Hojo’s work faded to insignificance. There was only this room, the quiet surrounding them, and the heartbeat tethered to his own.
When she stirred, murmuring something too soft to catch, he whispered the same words he had spoken in the lab, softer this time, meant only for her, as he had grown much softer this last month. “I’ve got you.”
The Red Thread glowed faintly in reply.
And though he would never name what he felt—not yet but soon—the warmth that lingered in his chest as the storm gathered outside was proof enough that it was real.
Whatever this was, he thought as he watched her hand unconsciously press to her abdomen, her lips parted in a sigh of relief.
Whatever this is, he continued his thought, I will not let it break her. Not now. Not ever.
@themaradwrites @craftyhal @kitcatling @prehistoric-creatures @creativechaosqueen
@chickensarentcheap @inkandimpressions @arrthurpendragon @projecthypocrisy @beyondnibelheim
@serenofroses @sapphirothcrescent @tolliver-j-mortaelwyver @blazerrigor @megandaisy9



















