Unlocking characters in Duet Night Abyss revolves around one of the most essential late-game mechanics — the Secret Letter System. Whether you’re aiming to build your dream team or unlock every character available, understanding how this system works will save you countless hours of confusion and wasted grinding. Here’s a full breakdown of how to farm, unlock, and optimize your character progression from level 40 onwards.
How the Secret Letter System Works
The Secret Letter System becomes available once you reach level 40, which naturally happens after completing the main story content available at launch. From this point, you’ll gain access to Secret Letter Clues, the key resource used to obtain character-specific secret letters.
You can earn Secret Letter Clues through nearly all major game activities — including:
- Main Story Quests
- Side Quests and Exploration
- Daily and Weekly Challenges
- General World Activities
Each Daily Quest rewards around 15 clues, so within two days you can gather roughly 30 clues, enough to trade for multiple secret letters of your desired character.
Once you have enough clues, head to the Exchange Menu to trade them for the Secret Letter corresponding to the character you want to unlock or upgrade.
Accessing Covert Operations
After acquiring Secret Letters, go to the Combat Menu and open Covert Operations. This is where the actual character farming missions take place.
Covert Operations are divided into three categories:
- Character Farming Missions
- Weapon Farming Missions
- High-Level Demon Wedge (Mod) Farming Missions
Each mission type rotates every hour, so the objectives and rewards constantly change. These missions may include defeating a certain number of enemies, defending structures, or eliminating high-priority targets.
Mission Duration and Efficiency
Most missions take between 40 to 90 seconds to complete once your characters are properly leveled. Even underpowered teams can finish runs in under 2 minutes. As your roster improves, these runs become faster and more efficient — many players can even AFK farm with strong AI companions handling the combat.
The key is learning which mission type your team performs best in, as not all have equal clear times or enemy types.
Secret Letter Rewards Explained
Each successful mission grants you three reward boxes — Bronze, Silver, and Gold — and you can choose one of the three each run.
- Bronze Rewards – Common resources or upgrade materials.
- Silver Rewards – Has a chance to drop 2 Character Shards.
- Gold Rewards – 10% chance to appear; contains 10 Character Shards.
Since each character requires only 30 shards to unlock, a few lucky gold rewards or consistent farming can unlock a new character in just a few runs.
There’s also a pity system, ensuring that even if your luck is poor, you’ll still earn shards steadily over time. The exact pity count isn’t confirmed, but it guarantees fair progression.
Farming New Characters
When a new character releases, their Secret Letter won’t be immediately available through clue trading. For the first few weeks or months, you can only obtain them through special modes before they’re added to the standard pool.
These are the main ways to farm new and future characters:
1. Immersive Theater (Monthly Cycle)
Endgame mode resetting every 28 days.
Features three difficulty tiers, each offering character and weapon rewards.
Completing nodes guarantees shards or full character unlocks.
Clearing the first and part of the second difficulty is enough to secure the new character each month.
Once the 28-day cycle ends, that character moves into the Nocturnal Echo reward pool.
2. Nocturnal Echo (Weekly Boss Mode)
Weekly challenge that can be cleared five times per week.
Rewards include Secret Letters, Character Shards, and Signature Weapons.
Great source for older event characters once they rotate out of Immersive Theater.
3. Mystic Maze (Roguelike Mode)
Weekly resetting roguelike mode with its own rewards.
Provides additional opportunities for secret letters and upgrade items.
Drop Rates and Farming Speed
Overall, the drop rates for Secret Letters and Character Shards are quite generous:
10% chance for a Gold box per mission.
2–10 shards per successful run depending on luck.
Consistent farming ensures steady progress without heavy RNG dependence.
In roughly an hour of focused gameplay, you can gather enough shards for a full unlock or significant progress toward a desired character.
Free vs. Paid Progression
While the system is free-to-play friendly, those looking to max dupe characters or fully refine signature weapons will need to invest significantly more time — or opt for paid shortcuts.
Still, the design ensures every player can unlock multiple characters without hitting hard paywalls, keeping the grind manageable and rewarding.
The Secret Letter System is the backbone of Duet Night Abyss’s progression loop. It’s fair, rewarding, and encourages consistent play across various game modes. Whether you focus on unlocking every character or powering up your favourites, the system provides multiple paths to reach your goals.