THE SAPPHIRE TRENCH: THE ENGINE OF AETHELIA
Welcome to the Sapphire Trench
What it is: The Sapphire Trench: The Engine of Aethelia is a deep-sea sci-fi adventure set in a bioluminescent underwater city. When the Great Engine that sustains the city's life fails, a Guardian must descend 2,000 meters into the midnight zone to repair the machinery and confront a massive, energy-leeching creature. The player must navigate high-pressure environments, flickering terminals, and treacherous ocean currents to restore power before the city’s oxygen runs out.
Tone & Feel: Deep-sea sci-fi · atmospheric · urgent · industrial · bioluminescent
Think pressurized diving suits, humming machinery, glowing coral gardens, dark oceanic trenches, and the rhythmic pulse of ancient technology.
Therapeutic Lens: Each scene is crafted to address specific cognitive and motor rehabilitation goals:
Executive Functioning: Planning character archetypes and sequencing complex override codes.
Working Memory: Recalling multi-step auditory instructions and complex navigation coordinates without notes.
Visual Processing: Scanning grids for specific symbols and discriminating targets within a visual field.
Fine Motor Control: Near-point copying of character data and non-dominant hand manipulation for "energy cell" calibration.
Sustained Attention: Maintaining focus during environmental hazards and multi-turn combat encounters.
Problem Solving: Making tactical choices under pressure and managing resource-based "hits" to health.
All clinical tasks are integrated into the underwater narrative, ensuring that therapeutic intervention feels like a high-stakes mission rather than a traditional exercise.
THE SAPPHIRE TRENCH: THE ENGINE OF AETHELIA: GM SCRIPT
For Occupational Therapists | Single-Client Session | Cognitive Rehabilitation
HOW TO USE THIS MODULE
● READ ALOUD: Read these sections verbatim to your client to build the world.
● GM DO THIS: Clinical instructions for setting up tasks or managing mechanics.
● SCRIPTED ROLLS: Use these specific phrases based on dice results to maintain the "vibe."
● Therapeutic Focus: Executive functioning (planning/sequencing), working memory, and sustained attention.
MATERIALS NEEDED (GM PREP)
● Game Tools: 2d6 dice, Character Sheet, Pencil.
● Therapy Materials (The "Engine Components"):
○ The Sequence Grid: A piece of paper with a 4x4 grid of random letters/numbers (Used for scanning and sequencing).
■ Provided at the end of the module
○ The Repair Map: A simple drawing of a submarine engine with 5 numbered parts (Used for working memory/following multi-step directions).
■ Provided at the end of the module
○ The Power Cells: 6-8 small items (coins, blocks, or beads) and a small container.
SCENE 1: THE HANGAR (character design)
Focus: Initiation, Planning, and Character Integration.
GM DO THIS:
1. Place the blank Character Sheet and a pencil in front of the client.
2. Present the Archetypes and Stats sheets in front of the client.
3. Instruct the client: "Copy the name, stats, and special power of your chosen hero onto your sheet." (This targets near-point copying and fine motor control).
READ ALOUD: "Deep beneath the crushing weight of the midnight zone lies Aethelia, a city of glass domes and bioluminescent gardens. You are a Guardian of the Trench, tasked with protecting the Great Engine that breathes life into the city. You stand in the flooded hangar, surrounded by humming machinery and the smell of ozone. Before you depart on your patrol, you must choose which Guardian path you follow. Your choice will determine how you handle the crisis ahead."
INSTRUCTIONS FOR CHARACTER SELECTION: (these three archetypes are what are recommended for this adventure, but you can allow your client to pick one of the others if appropriate)
● The Champion (Might +2, Agility +1): * Script: "You are the shield. You rely on strength and speed. Choose this if you want to solve problems with action and physical prowess."
○ Life: 4 Hits
● The Sage (Mind +2, Heart +1): * Script: "You are the scholar. You understand ancient tech. Choose this if you want to solve problems with logic, memory, and specialized knowledge."
○ Life: 2 Hits
● The Healer (Heart +2, Mind +1): * Script: "You are the stabilizer. You keep the systems—and people—running. Choose this if you want to solve problems with empathy and precision repair."
○ Life: 3 Hits
GM DO THIS: Ask: "As you pull on your pressurized diving suit, what is its signature color? Does it have a glowing visor or heavy armored plates?"
SCENE 2: SYSTEM FAILURE
Focus: Executive Functioning (Sequencing) and Cognitive Flexibility.
READ ALOUD: "A sudden, violent tremor shakes the hangar. The blue bioluminescence of the city outside turns a frantic, pulsing red. A mechanical voice echoes: 'CRITICAL FAILURE. OXYGEN FILTRATION STALLED.' The Main Engine has seized. You rush to the primary terminal, but the interface is a chaotic mess of symbols and flickering lights. To reboot, you must input the override sequence exactly as it appears in the manual."
GM DO THIS:
Place the Sequence Grid (a 4x4 grid of random letters/numbers) in front of the client.
READ ALOUD: “You rush to the primary terminal, but the interface is a chaotic mess of symbols and flickering lights. To reboot the system and restore the city's air, you must input the override sequence exactly as it appears in the emergency manual. You have 45 seconds before the backup power fails. Go!"
The Task: "You have 45 seconds to find and point to these symbols in order: 4 - B - 9 - K - 1 - X. You must scan the grid carefully; the safety of the city depends on your accuracy."
● If the client finds the sequence in under 45 seconds: Give them a +2 bonus to the following roll for their efficiency.
● If the client struggles or exceeds the time: They proceed to the roll with no bonus, as the system is now sparking and unstable.
READ ALOUD: "The screen is sparking and the glass is hot to the touch! You’ve located the override symbols, but the system is resisting. You need to enter the final stabilization command into the console. Roll 2d6 and add your Mind bonus to see if you can force the reboot."
GM SCRIPTED RESPONSES:
● ON A 10+ (SUCCESS): "The screen flashes a brilliant green! You hear the massive gears of the engine groan and then smooth out into a steady, powerful hum. The red emergency lights fade away, replaced by the calm blue glow of Aethelia. You’ve saved the city’s air supply…for now."
● ON A 7-9 (PARTIAL SUCCESS): "The engine restarts with a shuddering bang! You got the job done, but a nearby steam pipe bursts under the pressure. A spray of scalding mist hits your suit before you can jump back. You succeeded, but you take 1 Hit of damage from the heat. Mark that on your sheet."
● ON A 6 OR LESS (FAILURE): "The console shrieks and the screen goes black, you’re locked out! The digital override failed, and now the room is beginning to flood with icy seawater. Your only choice is to turn the heavy emergency bypass valves by hand. This is going to take pure physical strength. Roll 2d6 + Might to see if you can force them open before the water reaches your visor!"
○ MIGHT ROLL: 10+ (Success)
"With a roar of effort, you heave against the iron wheel. It resists for a moment, then spins with a metallic clang. The water immediately begins to drain as the mechanical bypass engages. You’re soaked and shivering, but the air starts flowing again. You survived by sheer force of will."
○ MIGHT ROLL: 7-9 (Partial Success)
"The valve is rusted tight! You throw your entire weight into it. It moves, but you feel a sharp pain in your shoulder as the metal finally gives way. The system reboots, but the physical strain has cost you. You succeed in saving the air, but take 1 Hit of damage from the exertion."
○ MIGHT ROLL: 6 OR LESS (Failure)
"The valve wheel snaps off in your hands! The room continues to flood, and the darkness is absolute. You’re forced to abandon the engine room and swim for the emergency hatch. You survive, but the engine is still broken, the city is now on its very last reserve of emergency oxygen. Things have just gotten much more dangerous. Mark 1 Hit of damage from the debris."
SCENE 3: THE DESCENT
Focus: Working Memory, Auditory Processing, and Sustained Attention.
GM DO THIS:
Place the Repair Map in front of the client.
The Priming Task: Tell the client: "We need to prime the engine for the high-pressure descent. Follow my instructions exactly." Give a 3-step auditory instruction (e.g., "Touch the Fuel Line 4, then the Pressure Valve 2, then the Core Reactor 1").
The Navigation Task: Once the engine is primed, give the navigation instructions verbally. Do not let the client write them down.
READ ALOUD: "The engine is idling, but the source of the tremor came from the Trench floor, 2,000 meters below. You climb into your 'Manta-Ray' class submersible. The hatch seals with a hiss, and the cabin lights dim to a soft amber.
As you begin your descent, the water turns from a pale turquoise to a pitch-black, lit only by your sub’s powerful headlights. Suddenly, the navigation computer begins to flicker and static fills your headset. HQ comes over the comms:
'Guardian, the interference is too strong! The GPS is down. Listen closely and repeat these coordinates back to me so I know you've got them: Dive 300 meters, Veer Right at the Giant Ribcage, and Hold steady through the Kelp Forest.'"
GM DO THIS:
● Ask the client to repeat the instructions back to you.
● BONUS LOGIC: * If they Succeeded at the Priming Task (Map): They get +1 to the Piloting Roll.
○ If they Succeeded at Repeating the Coordinates: They get another +1 to the Piloting Roll (Total +2).
READ ALOUD: "You push the throttle forward, feeling the pressure of the deep ocean pushing against the hull. The darkness presses in. Suddenly, the headlights catch a glimmer of massive, bleached bone rising from the silt, the Giant Ribcage. You’re at the crossroads where the path splits into three dark tunnels.
Even if you know the way, the currents here are treacherous, pulling at your hull like invisible hands. You must fight the controls to stay on course. Roll 2d6 + Agility (plus any bonuses earned)."
GM SCRIPTED RESPONSES:
● IF THEY REMEMBERED THE PATH CORRECTLY:
○ ROLL 10+ (Success): "You bank the sub to the right, gliding perfectly through the arch of the ancient ribs. You navigate the Kelp Forest like a ghost, arriving at the Power Hub without a scratch. You’re a natural pilot!"
○ ROLL 7-9 (Partial Success): "You know where to go, but a sudden thermal vent pushes you off course! You fight the wheel and make it through, but the stress drains you. You arrive safely, but take 1 Hit of damage from the mental strain of the struggle."
○ ROLL 6 OR LESS (Failure): "You know the way, but the sub doesn't respond! A mechanical glitch causes the craft to shudder and scrape against the Ribcage. You arrive at the Hub, but the hull is leaking. Mark 1 Hit of damage and take -1 to your next roll as you deal with the flickering dashboard."
● IF THEY FORGOT OR MISSED A STEP IN THE PATH:
○ ROLL 10+ (Success): "You aren't quite sure which tunnel was right, but your reflexes are incredible. You see the jagged rocks at the last second and pull a sharp maneuver that lands you right in front of the Power Hub. Talk about luck!"
○ ROLL 7-9 (Partial Success): "You hesitate at the crossroads and the current slams you into the side of the Ribcage. You manage to recover and find the right path, but the sub's frame is groaning. Mark 1 Hit of damage."
○ ROLL 6 OR LESS (Failure): "You veer into the wrong tunnel and head straight into a volcanic vent! The cabin temperature spikes and the sub takes a beating before you can back out. You eventually find the Hub, but you're limping. Mark 1 Hit of damage and take -1 to your next roll."
SCENE 4: COMBAT: THE CRYSTAL CRUSTACEAN (EXPANDED)
Focus: Planning, Multi-tasking, Fine Motor Control, and Problem Solving.
READ ALOUD: "The Power Hub is a massive spire of glowing blue energy, but it’s being strangled. A Crystal-Back Crab, the size of a house, is clamped onto the main line. Its shell pulses with stolen electricity, and as your lights hit it, a screech vibrates through your cockpit. It raises a massive, jagged claw. We are in combat!"
ROUND 1: THE INITIAL CLASH (Tactical Choice)
READ ALOUD: "The crab snaps its claw, trying to crush your cockpit! You have two choices: Blast it with harvester beams to crack the shell, or Maneuver to its blind spot. What’s the plan?"
● Choice A: Blast It (Might/Dexterity):
○ 10+: Direct hit! You crack a sapphire crystal. Crab loses 1 Hit.
○ 7-9: You hit, but its claw catches your hull. Both take 1 Hit.
○ 6 or less: You miss! The crab pins you. Take 1 Hit and you are "Restrained."
● Choice B: Maneuver (Agility/Mind):
○ 10+: You slip behind it. Gain +2 to your next roll.
○ 7–9: You get behind it, but a silt cloud obscures your vision. Gain +1 to next roll.
○ 6 or less: You're too slow. The crab spins and slams you. Take 1 Hit.
ROUND 2: THE SILT CLOUD (Environmental Hazard)
READ ALOUD: "The struggle has kicked up a massive cloud of black silt. You’re flying blind! Your sensors are screaming. You need to use your Acoustic Pinger to find the crab before it ambushes you."
GM DO THIS: Ask the client to close their eyes. Tap on the table in different spots. The client must point to where they think the sound is coming from.
● Success (2/3 correct): They find the opening. Roll Mind to strike. Crab loses 1 Hit.
● Failure: The crab strikes from the dark. Take 1 Hit.
ROUND 3: THE ENERGY OVERLOAD (The Therapy Task)
READ ALOUD: "The crab’s shell is glowing blindingly bright—it’s preparing an electrical pulse! If you can manually recalibrate your 'Power Cells,' you can create an opposite frequency to short-circuit its armor!"
GM DO THIS:
1. Place a small container and 10 small items (beads, coins, or blocks) on the table.
2. The Task: "Using only your non-dominant hand, move each cell into the container one at a time. You must finish in 30 seconds (or before the GM finishes a slow countdown)."
POST-TASK:
● Completed on time: The pulse shatters the crab's outer plating. Crab loses 1 Hit.
● Failed: The crab fires! Your systems reboot. Take 1 Hit and skip your next turn's bonus.
ROUND 4: CRITICAL DAMAGE (Problem Solving)
READ ALOUD: "The crab is leaking glowing fluid, but it's desperate. It grabs a heavy piece of the Power Hub's debris and prepares to hurl it at you. At the same time, your left engine is sparking! Do you Fix the engine to dodge, or Target the debris to blow it up?"
● Fix Engine (Mind/Dexterity):
○ Success: You zip away. The crab hits the seafloor, dazing itself. +2 to next roll.
○ Failure: The engine stalls. Take 1 Hit.
● Target Debris (Might/Dexterity):
○ Success: You blow the rock to pieces, peppering the crab with shrapnel. Crab loses 1 Hit.
○ Failure: You miss the rock. It slams your hull. Take 1 Hit.
ROUND 5: THE FINISH
READ ALOUD: "The crab is cracked and sparking. It’s wobbling on its legs, preparing one final charge. This is it, all power to the front cannons! Roll Mind or Dexterity with any accumulated bonuses!"
GM SCRIPTED RESPONSES:
● 10+: "The crab’s shell cracks wide open. It realizes it’s lost and scuttles away into the dark trench, leaving a trail of bubbles. You’ve done it!"
● 7–9: "The crab is driven off, but its final thrash knocks out your long-range scanners. You won, but you're limping home. Mark 1 Hit."
● 6 or less: "The crab withstands the blast! It slams into you. Roll Luck to see if your shields hold, or if you both go spinning into the abyss!"
CONCLUSION
READ ALOUD: "The Power Hub begins to glow with a steady, healthy rhythm once more. The city of Aethelia is safe. You pilot your sub back toward the surface, watching the lights of your home grow brighter. You saved the city today, Guardian. Power down your systems; you’ve earned a rest."
GM DO THIS: Briefly discuss with the client: "Which part of the mission required the most focus? How did your hero's strengths help you when things got stressful?"
Evidence:
While the effectiveness of TTRPGs in cognitive therapy have not been published at this time, the evidence available suggests a positive impact. Check out the Rehab Arcade’s TTRPG page for more information about this.
Below is evidence in support of the specific interventions used throughout this one-shot: