Secret Letters sit at the center of progression in Duet Night Abyss. You’ll spend them in Covert Commissions to roll for character Thoughts, weapon blueprints, and Demon Wedges. The loop is simple: gather Secret Letter Clues, exchange them for Secret Letters, run Commissions, and cash in the right drops. Here’s how the system actually works and the fastest ways to feed it.

What Secret Letters and Secret Letter Clues do

  • Secret Letter Clues are a currency. You exchange 10 Clues for 1 Secret Letter in the in-game shop.
  • Secret Letters are the ticket you bring into a Covert Commission (Character, Weapon, or Demon Wedge). After a clear, you pick one reward from three options pulled from that Letter’s pool.
  • Characters unlock from “Thoughts.” It takes 30 Thoughts for a new character. Gold-tier bundles of 10 Thoughts can drop, but they’re rare (10% chance).
  • Weapons and Demon Wedges unlock from a single blueprint drop, then you farm the associated materials—both come from the same Secret Letter pool.
Note: Covert Commissions are set at level 40. You can access them early in the story, but expect to gear up before you can farm them comfortably.

How to get Secret Letter Clues (most efficient sources)

Source Yield Cadence / Notes
Daily Commissions (Memos) 15 Clues at 200 Progress Daily; most reliable baseline
Mystic Maze 30 Clues Weekly
Immersive Theater Up to 280 Clues Per refresh; high-end challenge
Beginner’s Guide missions 1 Clue per mission Finite; one-time pool
Main story & major side quests Varies One-time; strong early-game source
Chests, achievements, events Varies Occasional; good supplemental income
Lunoeggy (dice purchase) Chance-based Not reliable; not recommended
Tip: Don’t skip dailies. At 15 Clues per day, you’re effectively earning a Secret Letter every two days even before weekly content.

Exchange Clues for Secret Letters (where to trade)

Trade Secret Letter Clues for Secret Letters in the Shop under the Covert Commissions tab. Each Letter costs 10 Clues. Pick Letters for the category you plan to run next (Character, Weapon, or Demon Wedge) to avoid wasting clears on the wrong pool.

Covert Commissions explained (how the drops work)

  • Categories: Character, Weapon, and Demon Wedge. You select a mission and consume one matching Secret Letter to enter.
  • Rotations: Objectives cycle hourly across categories. Rewards don’t change; only the mission format and length do.
  • End-of-run rewards: After a clear, you see three randomized items pulled from that Letter’s pool. You can take only one.
  • Character drop math: 30 Thoughts unlock a character. Gold-tier “10 Thoughts” rewards have a 10% drop chance, so expect multiple runs.
  • Weapon/Wedge path: One blueprint unlocks the craft. Required materials also come from the same Letter pool, so keep farming that category.
Tip: If you only care about a single goal (e.g., Thoughts), back out quickly from slow mission variants and requeue after the next hourly rotation to target faster objectives.

How character unlocks and upgrades fit together

  • Many characters are earned as you progress the main story. Everything else is accessible via Secret Letters in Commissions.
  • Beyond the initial unlock, you’ll continue using Secret Letters to chase Intron upgrades. These are significant power boosts—plan to keep farming even after you add a character to your roster.

New character availability windows (where their Letters appear)

  • Brand-new characters aren’t immediately in the shop. For the first 28 days, their Secret Letters are featured in Immersive Theater.
  • After that window, their Letters move into the Nocturnal Echoes weekly boss rewards.
  • Finally, their Letters are added to the shop’s exchange for Secret Letter Clues.

This staggered path makes it possible to target farm early—if you can clear the featured Immersive Theater stages at high ratings—or wait until they settle into weekly bosses and, later, the shop.

  • Every day: hit 200 Memo Progress for 15 Clues.
  • Every week: clear Mystic Maze for 30 Clues.
  • Chase Immersive Theater if you need a featured character’s Letters or a large Clue infusion.
  • Run Nocturnal Echoes for weekly Secret Letters tied to recent characters.
  • Spend Clues as you go; don’t hoard if you’re actively farming Thoughts or blueprints.

What not to do

  • Don’t bank on Lunoeggy’s dice. It’s chance-based and unreliable compared to guaranteed daily and weekly sources.
  • Don’t enter the wrong Commission category. Your Secret Letter determines the reward pool—match your goal before you queue.

If you keep the Clue pipeline flowing—15 from dailies, a weekly 30 from Mystic Maze, and periodic Immersive Theater bursts—you can feed a steady cadence of Secret Letters into Commissions. Stick to the category you actually need, accept that 10-Thought drops are rare, and the roster, weapons, and Wedges will fall into place over time.