Secret Letters are the backbone of progression in Duet Night Abyss. You exchange Secret Letter Clues for Letters, bring those Letters into Covert Commissions, and pick one of three rewards at the end of each run. Characters unlock with Thoughts, weapons, and Demon Wedges unlock with blueprints and materials, and all of it flows through the same loop.
Secret Letters, Clues, and commissions (what each does)
| Mechanic | How it works |
|---|---|
| Exchange rate | 10 Secret Letter Clues = 1 Secret Letter (choose Character, Weapon, or Demon Wedge) |
| Commission entry | Consume 1 matching Letter to start a Covert Commission; missions rotate hourly |
| End-of-run reward | Three randomized items from that Letter’s pool; take one |
| Character unlock | 30 Thoughts for a new character; 10‑Thought bundles can appear but are uncommon |
| Weapon/Wedge unlock | One blueprint unlocks the craft; required materials drop from the same Letter pool |
| Commission difficulty | Set at level 40; accessible early, but expect to gear up to farm comfortably |
Trial Rank matters. Clue drop rates increase as your Trial Rank rises, so your overall income improves as you progress. After Patch 1.2, Clue drop rates are higher in Immersive Theater and Nocturnal Echoes, shifting the optimal route toward those modes when they’re available.
Secret Letter reward drop rates (rarity and 10‑Thought odds)
When a Secret Letter rolls its three post‑mission rewards, items are weighted by rarity. Expect the following distribution across the pool:
| Rarity tier | Chance per roll |
|---|---|
| Common | 66.00% |
| Uncommon | 30.67% |
| Rare | 3.33% |
For character farming specifically, gold‑tier “10 Thoughts” rewards sit at roughly a 10% chance when they’re in the pool. You still need 30 Thoughts to unlock a character, so plan on multiple Letters and runs even with occasional 10‑Thought hits.
How to get Secret Letter Clues (daily, weekly, and burst income)
| Source | Typical yield | Cadence / notes |
|---|---|---|
| Daily Commissions (Memos) | 15 Clues at 200 Memo Progress | Daily baseline; don’t skip |
| Mystic Maze | 30 Clues | Weekly |
| Immersive Theater | Up to 280 Clues | Per refresh; high difficulty, best burst |
| Main story / major side quests | Varies | One‑time sources; strong early game |
| Beginner’s Guide missions | ~1 Clue per task | Finite pool |
| Achievements, chests, events | Varies | Occasional supplements |
| Nocturnal Echoes | Secret Letters (not Clues) | Weekly bosses; focuses on recent characters |
If you want raw speed outside of weeklies, running low‑level commissions repeatedly yields roughly 0.7–1.0 Clue per minute. That’s about 42–60 Clues per hour, or 4–6 Secret Letters per hour at the 10‑to‑1 exchange rate.
Faster farming: what to run and when
- Prioritize daily Memos for a guaranteed 15 Clues, then slot in Mystic Maze each week for a quick 30.
- Push Immersive Theater when you can clear it efficiently; it’s the highest burst of Clues per refresh and, post‑1.2, drops are richer.
- Use Nocturnal Echoes for weekly Secret Letters tied to the most recent characters.
- Between resets, spam short, low‑level commissions for 0.7–1.0 Clue per minute. If you only need Thoughts or a specific blueprint, back out of slow mission variants and re‑queue after the next hourly rotation.
New character availability windows (where their Letters appear)
Secret Letters for brand‑new characters follow a staggered path:
- First 28 days: featured in Immersive Theater.
- After 28 days: moved into Nocturnal Echoes weekly boss rewards.
- Later: added to the shop’s exchange for Secret Letter Clues.
If you have the team to score high ratings in Immersive Theater, you can target farm during that early window. Otherwise, they’ll cycle into weekly bosses and eventually the shop, where you can convert Clues directly.
Planning expectations for character unlocks
Character unlocks require 30 Thoughts. The pool includes single Thoughts and the rarer 10‑Thought reward at roughly 10%. Because commission rewards present only three pick‑one options per run, expect to funnel multiple Letters into repeated clears before you reach 30 Thoughts, even with occasional 10‑Thought hits. Weapons and Demon Wedges are more straightforward: once the blueprint drops, continued runs in that same category will feed the materials.
Common pitfalls to avoid
- Entering the wrong commission category. Your Secret Letter determines the reward pool—make sure it matches your target.
- Ignoring rotations. Objectives shift hourly; waiting out a slow mission type can speed up your loop materially.
- Relying on random dice purchases. Chance‑based options like Lunoeggy are inconsistent compared to guaranteed daily and weekly sources.
What this means for your weekly loop
- Daily: hit 200 Memo Progress for 15 Clues.
- Weekly: clear Mystic Maze for 30 Clues; run Nocturnal Echoes for Secret Letters tied to recent characters.
- As available: farm Immersive Theater for a large Clue injection and early‑window Letters.
- Between resets: run short commissions for 0.7–1.0 Clue per minute and convert at 10:1 into the Letters you actually need.
Stick to that cadence and respect the drop math: rarity skews toward Common, 10‑Thought hits are uncommon, and your Trial Rank steadily lifts Clue income. Over a few play sessions each week, that consistency unlocks characters, blueprints, and Wedges without wasted runs.
