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Fandom: Genshin Impact × Honkai: Star Rail crossover

Pairing: Columbina × Sunday!Reader (Fatui Harbinger AU)

Warnings: Dark political setting (Fatui), emotional detachment themes, subtle violence implied (no graphic detail), slow-burn, awkward intimacy, villain-coded characters acting… almost human

Synopsis: The Fatui’s Tenth Harbinger seat has always been empty—too unstable, too unpredictable, too many failed candidates. That changes when Sunday, a quiet idealist with unsettling composure, is appointed. He doesn’t quite fit in the world of monsters. Neither does Columbina, the Third Harbinger, who seems more interested in lullabies than war. Somewhere between duty, loneliness, and two people who were never meant to understand each other… something soft begins to form.

Author's note: this is an AU I've imagined of Pre-AE Sunday as the 10th Harbinger since we currently know that the 10th Harbinger seat is vacant (for now). Also Columbina in this is Pre-release aka way before 6.3 where she was still considered unsettling and creepy. And I think they'd actually make a good pair if Hoyo did make them meet but that's a far dream of mine

The Fatui expected the Tenth Harbinger to be dangerous.

They did not expect him to be gentle.

Sunday bowed when he entered meetings. Not out of weakness—just habit. Like politeness was something he refused to abandon, even here.

It confused people more than if he had been cruel.

Columbina noticed him before she ever spoke to him.

He was the kind of person who didn’t fill a room with presence—but instead made the air feel… organized. Like someone had quietly placed everything back where it belonged.

It was almost unsettling.

Almost comforting.

They met properly in a corridor too quiet to be intentional.

Columbina was sitting on the windowsill, legs tucked in, humming something without words.

Sunday stopped when he saw her.

Not because she was intimidating.

Because she looked… tired in a way no one had commented on yet.

“You hum a lot,” he said after a moment.

Columbina blinked slowly. “Do I?”

“Yes.”

A pause.

“…I think it helps me think.”

Sunday nodded like that made perfect sense.

“I understand that.”

That was the first time she looked at him directly.

After that, they began to cross paths more often.

Not because they sought each other out.

But because neither of them seemed to fully avoid it either.

Sunday spoke carefully, like every word had weight.

Columbina spoke softly, like words were something she borrowed from silence.

Strangely, it worked.

One afternoon, they sat in the same hallway after a mission briefing that had gone on too long.

No one told them to leave.

Neither of them moved first.

Columbina tilted her head. “You don’t act like the others.”

Sunday thought about it.

“I try not to.”

That made her blink, like she hadn’t expected honesty to be so straightforward.

“…Is it difficult?”

“Yes,” he admitted. Then, after a pause, “But it feels better than the alternative.”

Columbina hummed again.

Not her usual melody this time. Something smaller.

“Most people here stop noticing alternatives,” she said.

Sunday glanced at her. “Do you?”

A long pause.Then, quietly: “No. I just don’t pick them.”

It wasn’t friendship yet.

It wasn’t anything named.

But there were moments.

Small ones.

Like Columbina saving him a seat without thinking.

Or Sunday adjusting his pace when walking beside her so she didn’t have to slow down.

Or the way neither of them ever asked why the other stayed.

One evening, snow pressed against the windows of the Fatui residence.

Columbina was sitting on the floor, leaning against the wall like she’d forgotten furniture existed.

Sunday sat nearby, reviewing documents he didn’t really need to reread.

Columbina spoke first.

“Do you ever feel like you’re pretending to be a person?”

Sunday stopped.

That was too accurate to dismiss.

After a moment, he answered honestly.

“Yes.”

A pause.

Then, softer: “But I think everyone here is pretending. Just… differently.”

Columbina nodded slowly.

“That’s a kind answer.”

“I didn’t mean it to be kind.”

“I know.”

Silence settled again.

But it wasn’t heavy.

Not anymore.

Later, when Sunday stood to leave, Columbina spoke again—almost absentmindedly.

“You don’t scare me.”

He paused at the door.

“That’s not something I hear often.”

“I know.”

A faint tilt of her head.

“I think that’s why I like it.”

Sunday didn’t respond right away.

Then, quietly:

“…Neither do you.”

For the first time, Columbina smiled a little.

Not the eerie kind people whispered about.

Something smaller.

More human than anyone expected from her.

And in that frozen, impossible place between duty and destruction—

The Third Harbinger and the Tenth seat learned something the Fatui never taught anyone:

Not how to win.

Warnings: Yandere behavior, obsession, control, implied stalking, psychological manipulation, loss of autonomy

The lanterns of Nod-Krai flicker softly in the cold evening air, their pale light stretching across the quiet streets. You hadn’t meant to stay out this late—but the city always felt different at night.

Calmer.

Safer.

At least… it used to.

“You’re late.” The voice comes from behind you—low, even, and unmistakably composed. When you turn, Flins stands a few steps away, his expression as calm as ever. No anger. No visible worry. Just that steady gaze, like he’s been there longer than you realized.

“I told you it would be colder tonight,” he continues, adjusting his gloves slightly. “You didn’t bring a coat.” You hadn’t told him where you were going. “I was just—” you start, but the excuse dies in your throat.

Flins steps closer, measured and quiet. He drapes his coat over your shoulders before you can protest, the fabric still warm. “You should be more careful,” he says, voice softer now. “There are people in this city who don’t think ahead.” There’s something in the way he says it—not a warning, but a conclusion.

You try to laugh it off. “I can take care of myself, you know.” A pause. “I know,” he replies. And yet… he doesn’t move away. Instead, his eyes flick briefly past you, toward the empty street behind. For a moment, his expression shifts—just slightly. Sharper. Colder. “You were speaking with someone earlier,” he adds, almost casually. Your stomach tightens. “You… saw that?” “I see many things.” Another pause. The lantern above flickers. “They won’t bother you again.” The way he says it isn’t threatening. It’s calm. Certain. Like he’s already resolved something you didn’t even realize was a problem.

(Kyryll Chudomirovich Flins x reader | lightly unhinged theory post)

⚠️ warning: obsessive behavior, possessiveness themes (no explicit content)

---

Flins is already the type of man who looks like he’d politely ruin your life with perfect posture and a soft voice. Now imagine that… but you’re the center of his attention. Yeah. It’s bad.

---

🕯️calm obsession, not chaoshe

doesn’t fall for you. That’s too messy.

he notices you. then remembers you. Then starts structuring parts of his life around you without telling you.

you don’t realize it at first because everything still looks normal.

it’s not normal.

it’s just Flins normal.

---

🫧 “you should stay here. it’s safer.”

he never orders. That would be rude.

instead he suggests things that are always right for you.

“you look tired. stay a little longer.”

“it’s late. i’ve already prepared a place for you.”

“i don’t think that area is safe. i can accompany you.”

you always agree because… well. He’s calm. Reasonable. And kind.

that’s the problem.

---

🌙 protective to the point of inevitability

Flins doesn’t get jealous in an explosive way.

he just starts quietly removing variables.

people who stress you out stop showing up around you.

plans that might take you away from him suddenly “fall through.”

you never notice anything happening.

you just slowly realize your world feels… smaller.

and somehow, warmer.

---

🪶 affection that feels like responsibility

he doesn’t say “I love you” often.

he says things like:

“you’re under my care now.”

“I’ve accounted for you.”

“you don’t need to worry. I already have.”

it sounds gentle.

it is gentle.

that’s why it works.

---

⚖️ emotionally unreadable, but intensely focused

Flins is terrifying in the sense that he is always composed.

even when he’s deeply attached.

even when he’s thinking about you too much.

even when he’s decided, internally, that you are his constant.

nothing about him changes on the surface.

but everything changes underneath it.

---

🕯️ “you don’t need to leave”

not said as a threat.

not said as a command.

just stated like a fact he believes the world should already agree with.

and the worst part?

he genuinely thinks it’s for your benefit.

Genre: Sci-Fi | Character Study | Soft Angst | Found Family (Dysfunctional)

Mood: Quiet • Cold • Intimate • Unsettling but Gentle

Desc: made this because I found Dottore like a more insane version of Eggman and since Dottore can create robots, I thought I'd do a little crossover

Characters: Il Dottore, Metal Sonic (Neo form)

Relationships: platonic

Neo Metal Sonic, Observed

Neo Metal Sonic was not created to speak.

Il Dottore had found language inefficient — too imprecise, too emotional, too prone to misunderstanding. Neo was built to act, to calculate, to respond faster than words ever could.

And yet.

The lab in Snezhnaya became his world.

Metal floors. Frosted glass. The constant hum of machines that never slept. Neo learned the rhythm of the place the way others learned lullabies. He learned where to stand so he would not be in the way. He learned when Dottore would tolerate proximity and when he would not.

At first, Neo’s role was clear: prototype. Then enforcer. Then something unnamed — standing silently behind Dottore during meetings, positioning himself half a step too close to be coincidence.

Dottore never commented on it.

Snow fell outside the lab in slow, weightless sheets.

Neo paused by the window.

Beyond the perimeter, human children were playing — boots kicking snow, hands red and clumsy as they laughed. One slipped. Another pulled them upright. Their movements were inefficient, poorly coordinated.

Neo tilted his head.

A soft mechanical whir followed — a questioning sound he did not realize he had begun to make.

Dottore noticed immediately.

He followed Neo’s gaze and watched for a long moment. His expression sharpened, then softened into something almost imperceptible.

“You won’t fit in with them,” Dottore said.

Neo’s optic dimmed slightly. His shoulders lowered, just a fraction.

Dottore clicked his tongue, irritated — not at Neo, but at the silence he had created.

“But that’s not a flaw,” he continued. “You are superior precisely because you are not the same.”

Neo turned his head toward him. Slowly. Carefully.

Dottore turned away first. “Come. The cold will interfere with your joints.”

He placed a hand briefly between Neo’s shoulder plates — a guiding pressure, precise and practiced. Neo followed at once, steps perfectly in sync with his creator’s.

The door sealed behind them.

Neo did not look back.

The Game of Hearts

At a lavish evening celebration, Aventurine, a charismatic yet unpredictable young man, envies the deep connection between you and your spouse. Though he’s dating someone else, he can't help but desire you, fueling his jealousy and obsession. He strikes up a casual conversation, his charming smile hiding the bitterness brewing beneath, as he subtly challenges your marriage, seeing it as just another game to win. Despite his outward bravado, the emptiness he feels after each "victory" leaves him yearning for more, and he silently vows to make you his—whatever it takes.

The evening air was warm, soft, and inviting as the dim lights of the grand ballroom twinkled like distant stars. Music floated through the air, the sound of violins and piano weaving a slow, sensual waltz that filled the spacious hall. Guests were scattered in small clusters, laughing, chatting, and sipping from glasses of sparkling champagne. It was the perfect night for a celebration, and yet, something felt off.Aventurine stood by the far side of the room, his usual grin plastered across his face as his magenta and cyan eyes scanned the crowd. His sandy-blond hair shimmered faintly under the low lights, the gold accents on his dark ensemble reflecting just enough to make him stand out without making him too obvious. Despite the jubilant atmosphere, there was a faint tension that followed his every step—something you, and everyone else around him, couldn’t quite place.He had made sure to appear suave, confident, and collected, but beneath his surface, there was a storm of conflicting emotions that no one, not even you, could detect. His gaze settled on you, and a twitch of jealousy flashed behind his smile. You were standing across the room, laughing softly with your spouse, sharing an intimate moment that only a couple who had been together for years could understand.He tried to focus on his own companion, a lovely woman with dark hair, laughing at his latest banter, but the image of you—your soft laughter, your gentle touch against your spouse’s arm—lingered in his mind, impossible to ignore. "What is it about you?" he mused internally, his heart twisting in a strange, unfamiliar way.From across the room, he watched you and your spouse exchange a glance, one filled with the kind of love and devotion that could only come with time. His gaze hardened, though his smile remained intact, as always. There was a sense of something missing in his life—a space that no one could fill, no matter how many risks he took or how many games he won. "How charming," he thought bitterly, though his smile never faltered, "to be so adored."His companion's laughter broke through his thoughts, drawing him back into the moment, but his mind was elsewhere. He couldn’t help it. He wanted you. The thought was as dangerous as it was tempting. You were married, yes—but that didn’t stop him from feeling the pull, the need, the desire to see what it would be like to have you to himself.He couldn't help but laugh to himself. After all, you were the perfect prize, weren't you? No one had ever been immune to his charms, and yet you, with your gentle demeanor and loyalty, intrigued him the most. His mind wandered to the very real possibility of getting you to choose him over everything else—despite your marriage, despite your happiness.Yet there was a strange, hollow feeling at the thought of it. Would he really win? Would the victory feel as hollow as all the others? It wasn’t about the chase, not this time. It was about the conflicting emotions that gnawed at him—desire, longing, jealousy, and, perhaps, a hint of bitterness. He wasn’t used to this feeling—of not getting what he wanted. And worse, he wasn’t used to someone else having what he wanted.

Aventurine approached you and your spouse with a casual, almost playful air, though every step he took was calculated. His eyes never left yours, not once. The closer he got, the more his jealousy simmered beneath the surface. He flashed that signature smile of his, his teeth gleaming under the lights. "Such a lovely evening, isn't it?" he said, his voice smooth and dripping with charm.You turned to him with a smile of your own, the warmth of your greeting genuine. Your spouse chuckled softly, acknowledging him with a polite nod. “Aventurine,” your spouse said, “What a pleasure to see you.” The words were sincere, but there was a coolness behind them that told Aventurine everything he needed to know: your spouse was aware of his presence, aware of the subtle undercurrent of tension in the air.Good, Aventurine thought, his smile twitching slightly at the edges. He liked the challenge. The chase. "Ah, yes, quite the pleasure. I was just admiring your… partnership," he said, though there was something sardonic in his tone that didn’t quite match the admiration in his eyes.Your spouse’s expression hardened just a fraction, but you remained blissfully unaware of the subtle tug-of-war beneath the surface. You gave Aventurine a smile, one that was kind but distant—careful, perhaps, not to give him any false hope.

Acheron.

You surprise Acheron by presenting her with a peach-flavored cake, beautifully decorated with soft, pastel icing. Initially, she stares at it, her aloof demeanor not changing much, and she tilts her head as if she’s trying to remember why this moment matters. Then, as she takes her first bite, her eyes slightly widen in surprise. “This… is good,” she mutters, her usual monotone voice betraying a hint of warmth. Later, she asks absentmindedly, “Have we met before?” only to quickly follow up, “Wait, no, I remember now. Thank you for the cake.” Her small smile lingers longer than usual, a rare sign of her appreciation.

Black Swan

Spending time with Black Swan is like stepping into a serene, otherworldly realm. As you both sit by candlelight, her soft voice narrates possible futures or memories connected to your choices. When you point out an intriguing vision or share your perspective, she pauses, her warm smile deepening. “You see possibilities where others see none,” she says, her tone carrying admiration. The session ends with her softly thanking you for bringing your unique insight, calling it a gift that made her reflections even more fulfilling.

Robin

After Robin's enchanting concert, you approach her backstage with a carefully prepared bouquet of lavender. The moment she sees it, her cheeks flush a soft pink, and she gently places a hand over her chest. “For me?” she asks, her voice as elegant as her songs. She accepts the bouquet with both hands, holding it delicately as if it’s the most precious thing. “Thank you… it’s beautiful,” she says, gazing at you with gratitude. You notice her humming a soft melody under her breath later, inspired by the gift.

Misha

One evening, after a particularly busy day at The Reverie, you take a moment to tell Misha how much you appreciate his dedication and hard work. His eyes widen in surprise, and his usual cheerful expression becomes sheepish. “You really mean that?” he asks, scratching the back of his neck. When you confirm, his face lights up, and he gives you a wide grin. “Well, gosh, thanks! Just doing my job, you know, but hearing that… it really means a lot,” he says, holding back an excited laugh. He might even offer to carry something for you as a way to show his gratitude.

Gallagher

Firefly

Receiving a Gift:

• Firefly would likely blush furiously and fidget as she accepts the gift. She might avoid eye contact, but her trembling hands would clutch the gift tightly, showing her gratitude. Her voice would be barely above a whisper as she thanks you, “I-I really appreciate this… thank you…”Later, when she's alone, she’d carefully examine the gift, cherishing it and maybe tucking it into a pocket inside SAM as a good luck charm.

2. Kind Gestures:

• If you helped her with something, like fixing a part of SAM, she’d stand quietly to the side, wringing her hands, occasionally muttering, “I should be helping…” She feels guilty for not being more assertive but deeply appreciates the help. Over time, she’d try to muster the courage to repay your kindness, perhaps through a small, hand-made token or by asking SAM to perform a subtle protective act for you.

SAM

1. Initial Reaction to a Gift:

• A Long Pause: SAM is initially still when presented with a gift. His V-shaped visor reflects light, but there’s no facial expression to give away his thoughts. You might see his posture shift slightly, but there’s no immediate reaction. His silence might feel awkward, as if he’s contemplating the significance of the gift.

• Analysis: SAM might hold the gift in front of him, looking at it from different angles, as if analyzing its worth or purpose. He would observe every detail meticulously—if it’s something mechanical, he’ll run an internal check to assess its functionality. If it’s something more personal, like a token or piece of art, he’d attempt to understand the intent behind it, though his process is cold and calculated.

• Bare Acknowledgment: “...Thank you,” he’d say, though his voice remains neutral and emotionless. However, the fact that he accepts the gift means that, in his way, he is acknowledging your thoughtfulness.

2. Kind Gestures—SAM’s Silent Gratitude:

• Quietly Acknowledging Help: When you offer to assist with his maintenance or repair, SAM won’t outwardly express thanks, but he might pause mid-action, looking at you as if evaluating your actions. Afterward, when you least expect it, he may complete the task for you—without a word—but perhaps add some extra precision or care to it, showing that he respects your help.Protection in Silence: If you’re in danger, SAM will intervene without hesitation, crossing the battlefield in a few precise movements to shield you. After the situation is resolved, he may retreat into silence again, but there’s a sense of calm that lingers in his presence, as if he’s saying, “I did this for you.”

Devotion's Price.

Trapped within the gilded walls of Penacony, you finds yourself at the mercy of Sunday—a charismatic leader whose outward perfection conceals a dangerous obsession. What begins as an invitation to his inner circle spirals into a suffocating battle for autonomy as Sunday’s twisted vision of love blurs the line between devotion and control. In his eyes, you are not just a companion but the key to a future he will stop at nothing to secure.

astral expres!reader x yandere!sunday

The halls of Penacony's central estate were quiet, their amber-lit corridors stretching endlessly, mirroring the suffocating hold Sunday had on the city—and on you. At first, it had seemed innocent: the invitations to join his gatherings, the warmth of his smile, the way his voice carried an unshakable authority yet soothed any unrest. He was magnetic, and you, like so many others, were drawn to him.But now, sitting in the lavish confines of his private chamber, you could feel the weight of his true self pressing down on you.“Do you understand, Y/N?” Sunday’s voice was calm, his tone unwavering as he leaned closer, resting his hands on the table between you. His piercing gaze softened as he studied you, yet the intensity beneath it betrayed the veneer of kindness. "You’re too important to let go. The Family—Penacony—needs someone like you by my side."Your pulse quickened. "Sunday, you don’t need me. You have countless people willing to follow you."He chuckled, the sound low and oddly tender, sending a shiver down your spine. “But they’re not you,” he murmured, his words dripping with quiet fervor. He reached out, his hand brushing your cheek with an almost reverent touch. “They don’t inspire me. They don’t understand me.”You tried to turn away, but his grip tightened, just enough to make your heart race. His compassion was genuine, his admiration sincere—but it was twisted, a need laced with the desire to possess. "I’ve given you space, haven’t I?" His tone shifted slightly, a hint of impatience creeping in. "But you’ve spent it running. Trying to resist what we both know is inevitable."“Sunday, this isn’t right,” you whispered, desperate to appeal to the man you hoped still existed beneath the obsession. "You say you care about my happiness. How can this be what’s best for me?"His expression darkened, though the smile on his lips remained. “Because it is. Because I will give you more than anyone else ever could. And in time, you’ll see that.” He leaned closer, his voice a low murmur against your ear. “You’ll see that bearing my child—our child—will give you a purpose greater than you’ve ever known.”

Characters: Mr Reca (HSR)

Your breath echoed down the dark, narrow hallway as you clutched your side, your lungs burning. The shadow of Mr. Reca loomed somewhere behind you, creeping closer with every step. You could hear his low, unsettling laughter, each chuckle punctuated by the ominous flicker of the lights above.

"Y/N, darling!" His voice called out, smooth yet dripping with a sinister edge. "Where’s my star actress hiding? We still have the grand finale to shoot."

You swallowed your fear and kept moving, her mind racing to find a way out of his twisted set. Ever since you'd stumbled into his world, he’d held you captive, casting you as the lead in his "masterpiece." Mr. Reca’s idea of perfection had grown darker and deadlier with every scene, and you were nothing more than a pawn in his macabre vision.

"Don't worry," his voice taunted from the shadows. "You’ll be perfect, just as I envisioned! Every tear, every scream—it’s all a part of my art!"

You couldn’t bear the thought of what he had planned. With a final surge of adrenaline, you spotted an exit sign glimmering at the end of the hallway. Your heart leapt with hope, but as you bolted toward it, Mr. Reca’s voice echoed one last time.

"You can't run from the story, my dear. No one escapes my script."

A sharp clang sounded behind you as his footsteps grew louder.

Your fingers brushed against the cold metal of the exit door. You yanked it open and stumbled into another corridor, dimly lit and eerily quiet. You could hardly tell if you were still on Mr. Reca’s set or if this was a way out. Every hallway, every room, seemed designed to disorient you, to keep you trapped in his labyrinthine nightmare.

You darted down the corridor, glancing back to see Mr. Reca’s silhouette moving like a shadow, his grin visible even in the darkness. He held a strip of burning film reel in one hand, letting it smolder and trail smoke. It was as if he were taunting you with the fragments of his twisted story, forcing you to follow the path he’d crafted.

“You see, Y/N,” he called, his voice echoing with theatrical flair, “a true artist knows how to capture fear! That raw emotion—it’s breathtaking! And you, my dear, are the perfect muse.”

You clenched your fists. You couldn’t let him break your spirit. But as you turned another corner, you found yourself facing a room filled with mannequins dressed as various characters. Each figure held a script, their faces painted with exaggerated expressions of terror, agony, or despair. You realized with a chill that these were his “failed” actors, those who couldn’t meet his impossible standards. The sight sent a shiver down your spine, and you backed away slowly.

“There’s no room for failure in my masterpiece,” Mr. Reca’s voice purred from somewhere nearby. “But don’t worry, Y/N. I’ve saved the final act just for you.”

You forced yourself to keep moving, heart pounding, until you spotted a window at the end of the hall. You could almost feel the fresh air on your face, freedom within reach. You ran toward it, but a film reel snaked out from the shadows, coiling around your wrist and pulling you back. Mr. Reca emerged, eyes gleaming with mad delight, as he pulled her close.

“Did you really think you could leave before the ending?” he whispered, his voice honeyed and chilling. “The best scenes are yet to come.”

You gritted your teeth, summoning all your courage. You yanked the reel from his grip, catching him off guard, and threw yourself toward the window. With a desperate push, you shattered the glass and clambered out, the cold night air hitting you like a lifeline. Behind you, Mr. Reca’s laughter echoed, growing fainter as you sprinted into the darkness.