The universe pinged Jim with a very MMO-feeling notification:
QUEST COMPLETE: Help Your Rat Brothers
Reward: Level Up! Choose a Class.
Since he was a tiny sewer gremlin with a one-slot bag of holding, the options that popped up were… very rat-core.
The “class select” screen floated in his inner eye like every character creation menu he’d ever seen, all built around being small, sneaky, and living in the sewers:
Sewer Skulker – Stealth / Scout / Assassin-ish
You lean into being a tiny, hard-to-hit shadow that lives where no one looks.
Level 1 perks: Filth-Camouflage, Back-Nip, Narrow Escape.
Playstyle: Rat rogue. Scout ahead, listen in on secrets, assassinate things your size, avoid ever being in fair combat.
Swarmcaller – Leader / Proto–Rat King
You’re still just one rat, but something in your soul resonates with the whole swarm.
Level 1 perks: Pack Link, Coordinated Scurry, Squeak of Rallying.
Playstyle: Rat tactician. You’re the brains of the swarm, eventually evolving toward a proper Rat King.
Plague-Touched Acolyte – Healer / Debuffer / Filth-priest
Some sewer spirit, minor god, or big Rat Fate took notice when you yanked that slime out of the world.
Level 1 perks: Filth Resilience, Grimy Blessing, Whisper of Decay.
Playstyle: Rat cleric of filth. You keep the swarm alive and start tossing around disease and sewer-based miracles.
Scrap Savant – Item Nerd / Inventory Abuser
You lean all the way into your ridiculous 1-item-of-any-size pocket dimension.
Level 1 perks: Quick Stash, Intuitive Appraisal, Mutable Slot (Limited).
Playstyle: Rat heister/artificer-lite. You steal, smuggle, and safeguard things far bigger than yourself.
Gutter Hexer – Minor Caster / Occult Sewer Goblin
Somewhere between warlock and witch-rat, you tap ambient sewer magic and curses.
Level 1 perks: Hexing Glare, Gutter Spark, Sewer Sense.
Playstyle: Weird little caster. Squishy but tricky, using tiny spells to make enemies misstep while you scamper away.
Jim only hesitated for a second.
He looked at the burned rats huddling around him. He looked at the scorched stone where an alchemical hazard used to be. He looked inward at the single ridiculous fact of his new life:
He had a one-slot personal bag of holding and had already used it to yoink an entire crate of wine, hoover up a sewer-spanning alchemical slime hazard, accidentally become a miracle for some overworked tavern staff, and save a bunch of rats from being dissolved.
The system built this menu after watching him do that.
“…Yeah,” he thought. “I know what you want me to take.”
He mentally tapped Scrap Savant.
The UI flared, then collapsed into him like he had just inhaled a small, glowing spreadsheet.
CLASS CHOSEN: SCRAP SAVANT (Level 1)
Inventory-based abilities unlocked.
His awareness of the inventory slot sharpened. Before, it was just a box he could stuff things into. Now it felt… tunable, like a muscle he could flex different ways.
New text scrolled past:
? Quick Stash: You can store or retrieve your inventory item almost instantly. No more fumbling.
? Intuitive Appraisal: You get a little system “vibe check” when touching items now: dangerous, magical, valuable, volatile, etc.
? Mutable Slot (Tiny Split): Once per day, you can split your one big slot into two tiny slots for small stuff—keys, rings, coins, a scroll, a single potion vial. When you collapse them back, any overflow gets spat out in front of you.
Jim tested it.
He focused on the inventory square: Experiment mode.
The slime icon fuzzes in his view, then cleanly divides… and the system slaps his mental hand.
Warning: Current item exceeds “tiny” capacity. Cannot split while storing Massive Hazard Object.
Suggestion: Do not juggle apocalyptic sludge while experimenting with advanced features.
“Yeah, fair,” he thought. “I deserve that.”
He dismissed the split, letting the slot stay big for now. Later, when he wasn’t carrying a sewer accident, he could practice with pebbles and corks.
The Intuitive Appraisal hummed at the edge of his senses too, like a background process waiting for an item to poke.
He brushed his paw against a fragment of broken glass by the tunnel wall.
Item: Broken Bottle Shard
– Value: Trash
– Threat: Moderate (to soft paws, throats, and egos)
– Magic: None
It wasn’t verbose, but it was something.
He glanced at the rats around him. They were watching him in that way animals watch storms: alert, wary, convinced something bigger than them had just moved.
Scrap Savant didn’t scream “leader” the way Swarmcaller would’ve.
And honestly? That’s what Jim had always been good at: not being the paladin, but being the one who understood how all the pieces on the table fit together and then doing something clever with them.
GM turned rat turned loot-engine.
You might be reading a stolen copy. Visit Royal Road for the authentic version.
He squeaked a short reassurance—path clear, keep moving—and the injured rat who invited him deeper nodded and started forward again.
Rat #1 fell in at the back of the little procession, his mind ticking.
He was level 2 now. Tiny, fragile, damp, and still extremely mortal—but:
He could steal, store, or neutralize anything he could touch.
He could sniff out what was valuable or dangerous at a glance.
He was walking into a situation where “something in the sewers is changing.”
That was a terrible combination for everyone else and an excellent one for him.
The little procession of rats moves deeper into the dark, and Rat #1 pads along at the back, dripping filth and quietly trying not to think about the fact that his inventory currently contains “one sewer-wide mistake.”
The tunnel slopes down, then levels out. The air changes again: less of the surface city’s mixed stink, more concentrated sewer-core—old waste, mold, damp stone, and the dense background musk of “a lot of rats live here.”
They’re heading home.
The tunnel opens into a broader chamber, like the first one, but lived-in.
There’s a main flow of water down the center, sluggish and dark, with a broad stone ledge on one side and a narrower one on the other. A collapsed bit of brick and masonry has turned part of the far wall into a pile of rubble; water trickles through cracks that weren’t meant to be there.
On the wide ledge, tucked up against the wall, is the nest.
To a human, it would look like trash: a mound of shredded cloth, paper, straw, and stolen bits of burlap, threaded around with long, chewed strips of rope. To Jim, it looks like a miracle of engineering. There are tunnels through the mound, separate chambers, escape exits. He sees at least two levels of “floor.”
And rats. Dozens of them.
Pups, eyes still half-closed, squirming in the inner warmth. Older juveniles chasing each other in twitchy circles. Adults grooming, sleeping, standing watch on the edges. A whole tiny society, crammed into a damp wedge of stone between “everything” and “drown.”
As the burned and limping scouts return, the nest stirs.
Heads rise. Whiskers flare. A susurrus of squeaks ripples across the chamber: Back. Alive? Water? What happened? Who is that?
Jim suddenly becomes the center of attention.
A big rat—big by rat standards, which still isn’t impressive on the heroic scale, but enormous compared to him—clambers to the front of the nest. Scarred ears, missing chunk of tail, heavy shoulders. Patriarch, the body language says boss.
They sniff him once, long and deep, taking in everything: tavern-cellar dust, surface air, faint trace of chemical burn, and the scent of “same” wrapped around something… off.
The burned scout, the limper, squeaks a fast, tangled recounting that Jim’s overloaded brain translates on the fly:
Water turned bad. It hurt. Siv is gone. New rat came from above. New rat touched bad water. Bad water vanished. Path is open.
A hush falls through the nest. You haven’t known true awkwardness until you’ve been a six-inch isekai holding a pocket catastrophe while fifty rats stare at you like you might be a minor sewer deity.
Boss Rat studies him, head slightly tilted, whiskers forward.
The posture that follows is complicated. Some dominance (this is my nest). Some wary respect (you did a thing we can’t). Some suspicion (things that break the rules are often dangerous).
You are not from here, the body says. You smell of above and wrong things. But my children crossed because of you.
They shuffle forward half a paw-length, bringing nose almost to his.
You are welcome. For now.
Jim manages a dignified half-bow, which in rat amounts to lowering his head and not trembling.
He gets out of being eaten or expelled. Good start.
Once the social checkpoint is passed, normal nest activity resumes in a jittery, not-really-normal way. The injured are herded further in; pups squeak for warmth and reassurance; some adults go back on watch.
The smell of worry doesn’t fade though. It’s baked into the walls.
Jim edges along the ledge toward the far side of the chamber, following a different stink: scorched stone, faint sharp-metal air, and the ghost of the same alchemical reek the slime had.
There.
Near the rubble pile, at the edge of the main channel, he finds ground zero.
The stone is blackened and eaten away in a rough circle, like something corrosive splashed out in all directions. The bricks in the wall above are cracked and discolored. A long smear of melted… something… leads from the scorch mark to the water, like a line of wax drippings.
At the center, half-submerged in an eddy of filth, is part of a barrel hoop—iron band, twisted and corroded.
He pads closer and taps it with a claw.
UI flicker.
Item: Corroded Barrel Hoop
– Value: Scrap
– Threat: Low (physically)
– Residue: Alchemical Spill (faded)
– Origin: Surface manufacture. Not sewer-native.
Somewhere above this chamber, someone was storing or transporting barrels of something very wrong. One fell. Broke. Dumped poison into the nest’s main path. The slime he pocketed earlier was the secondary flow, washed downstream and collecting in low spots.
GM-brain sketches a little mental map: surface warehouse → cracked floor or shunted waste pipe → this chamber → downstream slime basin.
So it’s not the sewer deciding to hate us, he thinks. It’s someone topside treating the sewer like a garbage can.
Classic.
He lifts his nose, sniffing higher, trying to pull any hint of whose garbage this was through a layer of stone. The Intuitive Appraisal burbles at the edge of his senses but can’t do much with faint smell alone. All he gets is “same as the slime” and “wizard-lab-adjacent energy.”
Which narrows it down in Waterdeep to, what, five thousand suspects.
Still: it’s a vector.
Back at the nest, the boss rat has gathered a little cluster of elders: older, scarred animals with the slow, measured movements of creatures who’ve survived enough to take life seriously.
Jim approaches cautiously, making himself small.
The limper from earlier is there too, leg tucked up, watching.
The patriarch sniffs him again, then gestures with their head toward the downstream tunnel—the one that leads away from the slime basin, further from the city, toward the deep sewer web.
We move soon, their posture says. This place is not safe now. Water changed. Stone broken. More bad might come from above.
The elders erupt in a flurry of squeaks and sharp tail flicks.
The oldest one, fur patchy and eyes milky, bristles. Curse. All of it curse. The deep gods are angry. The water itself punishes us for living too close to the two-legs. We must flee or the rot will take every pup.
A lean, wiry elder with a torn ear snaps back, ears flat. Food paths are cut. Three days since the last good scavenging run. We stay and we starve slow. We move and we at least have a chance. Risk is risk—staying is worse.
A stocky, battle-scarred male rears up slightly, teeth bared in challenge. This is our territory! The pipes, the ledges, the flow—all ours. Some surface filth dares poison our home and we run? We should find the source and bite it until it stops.
The patriarch lets them argue for a moment, then silences them with a low, rumbling chitter. The body language is tired but firm.
We can fight other rats. We can run from big things. We cannot fight stones that melt and water that burns.
They look back at him, eyes dark and very, very aware that what he did is not normal.
Can you stop it if it comes again?
Jim swallows.
His inventory slot, somewhere in the metaphysical midbrain, quietly radiates you are holding the problem, not a solution.
He could, theoretically, remove more slime if it appears. But if the source is some alchemist’s ongoing waste disposal, he’d just be unplugging leaks while someone keeps pouring. And his slot is one item only; there’s a limit to how many angry puddings you can juggle.
He answers with careful body language:
I can stop some. Not all. Not always.
The boss rat studies him for a long, still moment.
Then we move. And you… you find why the water changed.
He hadn’t exactly signed up for “tiny sewer detective,” but it sat… weirdly comfortably. In his old life he was the DM dropping quest hooks on players. In this one the NPCs were dropping one on him — and they all had whiskers.
He nodded. Tail steady, ears forward.
I will look. From above and below.
