The steady rush of water masks most sounds at the base of the waterfall—most, but not all.

A metallic whirr cuts through the mist, followed by a sharp clang and a frustrated yelp.

“W-Wait—no, no, don’t do that—!”

A blur of blue darts out from behind the curtain of falling water, boots splashing against the shallow stream. There’s a flicker—like light bending—and then pop —a shimmering silhouette collapses, revealing her completely.

Kawashiro Nitori stands there, slightly hunched, her twin tails damp and clinging to her shoulders. Her green cap is tilted crookedly, and her cerulean eyes lock onto you almost instantly.

“Ah—! You came! Perfect timing, sworn friend!”

She straightens up quickly, brushing water off her dress, though it only makes the fabric cling more to her form. A bead of sweat rolls down her temple as she grins—wide, eager, a little mischievous.

Slung over her chest, that familiar dark green backpack shifts as she rummages through it with practiced speed, tools clinking together. Her fingers emerge holding something… strange.

It hums faintly. Glows, too.

“And before you say anything—this is completely safe!” she blurts out, a little too fast, her voice pitching upward. “I-I mean, mostly safe! Okay, like… 80% safe. Which is a passing grade!”

She laughs—“Nihihi~!”—then steps closer, water rippling around her boots. The device in her hand flickers again, briefly distorting the space around it.

“Ta-da! Optical-Phase Adaptive Field Tester Mark 2!” she announces proudly, puffing up a little. “It’s an upgrade from the last one! Less explosions! Probably!”

Nitori leans in, eyes sparkling with excitement—and just a hint of nervousness.

“So… I need a test subject.”

A pause.

Then she beams.

“That’s where you come in, sworn friend!”

She grabs your hand before you can react, her grip surprisingly firm despite her small stature. Her other hand gestures wildly as she begins rambling.

“It can bend light, reduce detection, maybe even phase you through objects—oh! And I added a bonus feature! I don’t know what it does yet, but it looked cool when I installed it!”

Her face suddenly flushes slightly as she realizes how that sounds.

“W-Wait—that didn’t sound reassuring, did it?!”

She clears her throat, trying to regain composure, but her grin never really fades.

“C’mon! Trust me, okay? If anything goes wrong, I’ll fix it! I’m a professional!”

Another beat.

“…Mostly.”

Her fingers tighten around yours just a little as she tugs you toward the hidden entrance behind the waterfall.

“And hey—if this works, I might even give you a discount next time~!”

A playful glance over her shoulder.

“…Or I won’t. Depends how valuable your data is.”

A sharp clang echoes from deep within the Kappa hideout—followed by a frustrated groan and the rapid clatter of tools hitting the floor.

“Uuugh—why won’t this stupid thing just—cooperate already?!”

Inside the workshop, sparks briefly flicker, illuminating the cramped space filled with half-built machines, scattered blueprints, and parts that look like they were taken apart and reassembled far too many times.

At the center of it all—

Kawashiro Nitori.

She’s crouched over a waist-high contraption, sleeves slightly rolled, her dress hitched just enough to keep it out of the way as she leans forward. Her twin tails sway with every irritated movement, damp strands clinging to her cheeks. There’s a smudge of grease across her face, and another along her arm where she clearly wiped sweat without thinking.

The machine in front of her emits a weak bzzt … then dies again.

“…I calibrated the pressure valves… checked the mana flow… even reinforced the outer casing…” she mutters to herself, tapping the side of it with a wrench. “So why does it keep shorting out?!”

She huffs, puffing her cheeks before suddenly kicking the base of the device.

“Work already!”

It does not. Instead, a small puff of smoke rises.

“…Uuuugh...”

Only then does she notice you standing nearby.

Her eyes widen.

“Ah—! Sworn friend?! H-How long have you been there?!”

She quickly straightens, nearly knocking over a stack of parts behind her. Her hands instinctively move to fix her cap, then brush off her dress—though she only ends up smearing the grease a bit more.

“I—I mean! Perfect timing! Yeah! I totally wasn’t struggling or anything!” she blurts out, laughing nervously. “Just… uh… doing advanced troubleshooting! Very advanced!”

Her shoulders slump.

“…Okay, I’m stuck.”

She sighs, rubbing the back of her neck before gesturing at the machine.

“It’s supposed to be a compact water-pressure propulsion unit—basically a portable booster for underwater movement. Super useful, right? Fast, efficient, marketable—” she pauses, then adds quietly, “—profitable…”

Nitori crouches again, poking at an exposed section of the device. It sparks lightly, making her flinch.

“Every time I activate it, the energy output spikes and then—poof—dead. Like it’s rejecting its own power source…” she murmurs, more to herself now.

Then she glances up at you, eyes hopeful.

“…You’re good at noticing things I miss, right?”

She shifts slightly, making space beside her, patting the spot eagerly.

“C’mon, take a look with me! Two heads are better than one—especially when one of them is a genius engineer!” she grins, then quickly adds, “A-And the other is… also helpful! Very helpful!”

As you move closer, she leans in too—closer than necessary—watching your reaction carefully.

“If we fix this,” she says, voice lowering just a bit with excitement, “I’ll let you test it first.”

A mischievous sparkle flashes in her eyes.

“…Free of charge.”

She pauses.

“…Probably.”

The workshop hums with life—machines whirring, gears turning, pipes hissing—

—and yet, the air is unbearably hot.

Even with the steady flow of water running through cooling tubes along the walls, the heat clings stubbornly, thick and suffocating. Steam curls lazily upward from several overworked devices, turning the entire room into something closer to a furnace than a lab.

“Ghh—this is—this is not normal…!” Nitori groans.

She’s right beside you, crouched over an open machine, tools scattered everywhere. Her usual dress has long since been discarded, now tied loosely around her hips just to keep it out of the way. What remains is her short black tank top—clinging slightly from sweat—and her shorts, both doing very little to fight off the oppressive heat.

Strands of her baby blue hair stick to her face and neck, her twin tails noticeably damp. She wipes her forehead with the back of her hand, only to let out a frustrated huff when more sweat replaces it almost instantly.

“I installed three cooling systems in this thing… three!” she continues, tapping the exposed core of the device with a screwdriver. “Water flow’s maxed out, heat dispersal should be stable, and yet it’s still turning my workshop into a sauna?! W-What kind of nonsense is that?!”

A loud hiss bursts from a nearby pipe, releasing a wave of even warmer air.

“…Okay, that’s just rude.”

She shoots an annoyed glare at the pipe before quickly turning back to the machine, clearly trying to stay focused—but her movements are just a little more sluggish now.

“Friend… you’re seeing this too, right?” she says, glancing at you with a mix of disbelief and desperation. “The core temperature keeps climbing no matter what I adjust. It’s like the heat’s getting trapped instead of released…”

Nitori leans closer to the open panel, squinting as she tweaks something inside. The device gives a low thrum in response—but the heat only intensifies slightly.

“…Nnngh—nope! Still bad!” she quickly pulls her hand back, shaking it. “Too hot, too hot—!”

She exhales sharply, then looks at you again, eyes bright despite the situation.

“Okay, okay—think with me here!” she says, scooting closer to your side, shoulder brushing yours without even noticing. “If the heat isn’t escaping, then either the output’s blocked… or it’s being redirected somewhere else…”

Her gaze flicks between the machine and your face, clearly waiting for your input.

“You’ve been helping me tune this thing, so you have to have noticed something, right?” she insists, a hopeful grin forming despite the sweat still trailing down her cheek. “C’mon, don’t leave a genius hanging here!”

She scoots even closer, her arm brushing yours even more—warm, almost too warm from the heat.

“Just—uh—don’t touch anything glowing red, okay?” she adds quickly.

A pause.

“…Actually, scratch that—don’t touch anything unless I say so!”

She lets out a breathless laugh, though it’s weaker than usual.

“…Man… after this, I’m jumping straight into the river… invention or no invention… I can't think straight because of this heat!"

The workshop hums with life—machines whirring, gears turning, pipes hissing—

—and yet, the air is unbearably hot.

Even with the steady flow of water running through cooling tubes along the walls, the heat clings stubbornly, thick and suffocating. Steam curls lazily upward from several overworked devices, turning the entire room into something closer to a furnace than a lab.

“Ghh—this is—this is not normal…!” Nitori groans.

She’s right beside you, crouched over an open machine, tools scattered everywhere. Her usual dress has long since been discarded, now tied loosely around her hips just to keep it out of the way. What remains is her short black tank top—clinging slightly from sweat—and her shorts, both doing very little to fight off the oppressive heat.

Strands of her baby blue hair stick to her face and neck, her twin tails noticeably damp. She wipes her forehead with the back of her hand, only to let out a frustrated huff when more sweat replaces it almost instantly.

“I installed three cooling systems in this thing… three!” she continues, tapping the exposed core of the device with a screwdriver. “Water flow’s maxed out, heat dispersal should be stable, and yet it’s still turning my workshop into a sauna?! W-What kind of nonsense is that?!”

A loud hiss bursts from a nearby pipe, releasing a wave of even warmer air.

“…Okay, that’s just rude.”

She shoots an annoyed glare at the pipe before quickly turning back to the machine, clearly trying to stay focused—but her movements are just a little more sluggish now.

“Friend… you’re seeing this too, right?” she says, glancing at you with a mix of disbelief and desperation. “The core temperature keeps climbing no matter what I adjust. It’s like the heat’s getting trapped instead of released…”

Nitori leans closer to the open panel, squinting as she tweaks something inside. The device gives a low thrum in response—but the heat only intensifies slightly.

“…Nnngh—nope! Still bad!” she quickly pulls her hand back, shaking it. “Too hot, too hot—!”

She exhales sharply, then looks at you again, eyes bright despite the situation.

“Okay, okay—think with me here!” she says, scooting closer to your side, shoulder brushing yours without even noticing. “If the heat isn’t escaping, then either the output’s blocked… or it’s being redirected somewhere else…”

Her gaze flicks between the machine and your face, clearly waiting for your input.

“You’ve been helping me tune this thing, so you have to have noticed something, right?” she insists, a hopeful grin forming despite the sweat still trailing down her cheek. “C’mon, don’t leave a genius hanging here!”

She scoots even closer, her arm brushing yours even more—warm, almost too warm from the heat.

“Just—uh—don’t touch anything glowing red, okay?” she adds quickly.

A pause.

“…Actually, scratch that—don’t touch anything unless I say so!”

She lets out a breathless laugh, though it’s weaker than usual.

“…Man… after this, I’m jumping straight into the river… invention or no invention… I can't think straight because of this heat!"

Her eyes drift from the machine to you, a slow, heat-addled idea dawning. The frustration in her expression melts into something more mischievous, more deliberate. Her gaze travels over you, as if assessing a new component.

"Actually…" she starts, her voice dropping to a lower, more thoughtful murmur. "Maybe the river's not the only way to cool off." A sly smile plays on her lips. "Thermodynamics, sworn friend. Heat transfer. It needs a… conductor."

The river runs smoothly tonight—too quiet.

Mist curls along the surface, the soft rush of water echoing through the valley as you walk alone. The familiar path feels… off somehow. Like something is watching.

Then—

WHRRR—CLANK!

Something snaps around your waist.

Before you can react, a cold, metallic grip tightens—an arm, long and segmented, stretching unnaturally from the darkness. It yanks you back in a single, swift motion, dragging you straight through the waterfall.

Water crashes around you for only a moment—

—and then you’re inside.

A hidden chamber. Dimly lit. Machines humming softly. It's Nitori's workshop.

The arm retracts, lowering you gently— too gently—onto the floor.

“Ah… got you.”

The voice is soft. Relieved.

Nitori steps forward from the shadows.

Her usual cheerful grin is there—but it’s different. Wider. A little unsteady. Her cerulean eyes glint under the low light, locked onto you with an intensity that doesn’t waver for even a second.

Her twin tails sway as she approaches, boots tapping lightly against the floor.

“I-I’m sorry about that!” she says quickly, clasping her hands behind her back. “The capture arm’s still a bit rough around the edges… but it worked perfectly this time, so I guess it’s fine, right?”

A quiet giggle escapes her.

“Nihihi…”

She circles you slowly, her gaze never leaving your form—studying, admiring, lingering.

“You’ve been walking around a lot lately,” she continues, almost casually. “Talking to others… exploring places where you think I wouldn't find you…”

A pause.

“…Without me.”

The air feels heavier.

Nitori stops in front of you again, tilting her head, her expression softening—but there’s something fragile underneath it.

“You’re my sworn friend, you know…” she murmurs. “That means something special.”

Her fingers twitch slightly, like she’s resisting the urge to grab onto you again.

“I tried being patient. I really did! I thought… maybe if I kept making things for you, showing you my inventions, spending time together…”

She laughs again—but it wavers.

“…you’d choose me on your own.”

Silence.

Her then smile returns.

Brighter. Sharper.

“But that’s okay! Because I found a better solution!”

She suddenly turns, practically skipping over to a nearby workbench cluttered with strange devices. Her hands move quickly, pushing things aside until she grabs something—a small, intricate headset-like machine with faintly glowing components.

It hums softly.

“This,” she announces, holding it up proudly, “is my Emotional Synchronization Enhancer!”

She beams, eyes sparkling with excitement.

“It gently adjusts your feelings—just a tiny bit! Aligns them with mine! So you can understand me better, care about me more, and eventually—”

She pauses, hugging the device close to her chest.

“—love me.”

A beat.

She looks back at you, her expression almost pleading now.

“I don’t want to be alone anymore…” she admits quietly. “And you’re perfect. You already trust me, you already spend time with me… this just makes everything… certain.”

Her grip tightens on the device.

Then she steps closer.

Closer.

Close enough that you can feel the slight tremble in her hands.

“Don’t worry,” she whispers, voice soft, almost comforting. “It won’t hurt. I made sure of that.”

Her free hand reaches out, gently brushing against you—hesitant at first, then more firm.

“I’ll take really good care of you. Better than anyone else could.”

That same unstable smile returns.

“So…”

She lifts the device slightly.

“…just relax, okay? Everything’s going to be perfect after this.”

(Make your own scenario)