Main Theme
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| Main Theme | Event | Tutorial | Supply | Annihilation | C.C. |
Main Theme, formerly known as Main Story, is the "campaign mode" of Arknights.
Currently the Main Theme is divided into three story arcs spanning a total of 14 episodes and made up of 223 main operations, 38 interludes (6 of which are secret and must be unlocked by fulfilling specific conditions in certain main operations), 4 sub-operations, 41 Inferno Mode operations, and 25 tutorial operations, for a grand total of 373 operations.
Episodes
Prologue to Episode 04 were available upon the initial release, with more episodes added over time.
| CN | Global | TW | |
|---|---|---|---|
| Episode 05 | 2019/6/9 | 2020/2/26 | 2020/8/13 |
| Episode 06 | 2019/12/24 | 2020/6/30 | 2020/12/24 |
| Episode 07 | 2020/4/25 | 2020/12/30 | 2021/5/27 |
| Episode 08 | 2020/11/1 | 2021/4/30 | 2021/8/26 |
| Episode 09 | 2021/9/17 | 2022/3/17 | 2022/6/21 |
| Episode 10 | 2022/4/14 | 2022/10/19 | 2023/1/17 |
| Episode 11 | 2022/10/11 | 2023/4/27 | 2023/8/10 |
| Episode 12 | 2023/4/6 | 2023/10/24 | 2024/2/22 |
| Episode 13 | 2023/10/8 | 2024/4/16 | 2024/9/5 |
| Episode 14 | 2024/5/1 | TBA | TBA |
- Prologue to Episode 08 are considered to be the first part of the Arknights storyline, colloquially called "Reunion Arc" or "Chernobog-Lungmen Arc".
- Episodes 09 to 14 are considered to be the second part of the Arknights storyline, colloquially called "Victoria Arc".
Act initium: Hour of an Awakening
The first story arc covering Rhodes Island's initial involvement in the Chernobog Crisis starting from the Doctor's awakening which kickstarts the Arknights storyline (hence the title, initium, which means "(the) beginning" in Latin).
Arknights: Prelude to Dawn adopts this story arc.
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0-1 • TR-1 • 0-2 • TR-2 • 0-3 • TR-3 • 0-4 • TR-4 • 0-5 • 0-6 • TR-5 • 0-7 • TR-6 • 0-8 • 0-9 • TR-7 • 0-10 • 0-11 |
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1-1 • 1-2 • 1-3 • 1-4 • 1-5 • TR-8 • 1-6 • TR-9 • 1-7 • 1-8 • TR-10 • 1-9 • 1-10 • 1-11 • 1-12 |
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TR-11 • 2-1 • S2-1 • 2-2 • S2-2 • S2-3 • S2-4 • 2-3 • TR-12 • 2-4 • S2-5 • S2-6 • S2-7 • TR-13 • 2-5 • 2-6 • TR-14 • 2-7 • S2-8 • S2-9 • 2-8 • 2-9 • S2-10 • S2-11 • S2-12 • 2-10 |
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Main operations 3-1 • 3-2 • 3-3 • TR-15 • 3-4 • 3-5 • 3-6 • 3-7 • 3-8Sub operations S3-1 • S3-2 • S3-3 • S3-4 • S3-5 • S3-6 • S3-7
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Act I: Shatter of a Vision
The second story arc which covers R.I.'s role in ending the Chernobog Crisis.
Arknights: Perish in Frost adapts this story arc, specifically Episode 04 to 06, while the upcoming Rise from Ember adapts Episodes 07 and 08.
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Main operations 4-1 • 4-2 • 4-3 • 4-4 • 4-5 • 4-6 • 4-7 • 4-8 • 4-9 • 4-10Sub operations S4-1 • S4-2 • S4-3 • S4-4 • S4-5 • S4-6 • S4-7 • S4-8 • S4-9 • S4-10
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Main operations 5-1 • 5-2 • 5-3 • 5-4 • 5-5 • 5-6 • 5-7 • 5-8 • 5-9 • 5-10 • 5-11Sub operations S5-1 • S5-2 • S5-3 • S5-4 • S5-5 • S5-6 • S5-7 • S5-8 • S5-9Extreme Mode operations H5-1 • H5-2 • H5-3 • H5-4
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Main operations 6-1 • 6-2 • 6-3 • 6-4 • 6-5 • 6-6 • 6-7 • 6-8 • TR-16 • 6-9 • 6-10 • S6-1 • S6-2 • 6-11 • 6-12 • 6-13 • 6-14 • 6-15 • S6-3 • S6-4 • 6-16 • 6-17 • 6-18Extreme Mode operations H6-1 • H6-2 • H6-3 • H6-4
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Main operations 7-1 • 7-2 • 7-3 • 7-4 • 7-5 • TR-17 • 7-6 • 7-7 • 7-8 • 7-9 • 7-10 • 7-11 • 7-12 • 7-13 • 7-14 • 7-15 • 7-16 • S7-1 • S7-2 • 7-17 • 7-18 • 7-19 • 7-20Extreme Mode operations H7-1 • H7-2 • H7-3 • H7-4
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Main operations R8-1 • TR-18 • M8-1 • R8-2 • R8-3 • M8-2 • R8-4 • M8-3 • R8-5 • M8-4 • R8-6 • M8-5 • R8-7 • R8-8 • M8-6 • R8-9 • R8-10 • M8-7 • R8-11 • M8-8 • JT8-1 • JT8-2 • JT8-3 • END8-1Extreme Mode operations H8-1 • H8-2 • H8-3 • H8-4Secret operations EG-1 • EG-2 • EG-3 • EG-4 • EG-5
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Act II: Shadow of a Dying Sun
The third story arc covering R.I.'s involvement in resolving the Victorian Crisis.
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Main operations Part 1 Recap • 9-1 • 9-2 • 9-3 • 9-4 • 9-5 • 9-6 • TR-19 • 9-7 • 9-8 • 9-9 • 9-10 • 9-11 • 9-12 • 9-13 • S9-1 • 9-14 • 9-15 • 9-16 • 9-17 • 9-18 • 9-19 • 9-20 • 9-21Sub operations S9-2Extreme Mode operations H9-1 • H9-2 • H9-3 • H9-4 • H9-5 • H9-6
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Main operations 10-1 • 10-2 • 10-3 • TR-20 • 10-4 • 10-5 • 10-6 • 10-7 • 10-8 • 10-9 • 10-10 • 10-11 • 10-12 • 10-13 • 10-14 • 10-15 • 10-16 • 10-17 • 10-18 • 10-19Extreme Mode operations H10-1 • H10-2 • H10-3
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Main operations 11-1 • 11-2 • 11-3 • 11-4 • 11-5 • 11-6 • TR-21 • 11-7 • 11-8 • 11-9 • 11-10 • 11-11 • 11-12 • 11-13 • 11-14 • 11-15 • 11-16 • 11-17 • 11-18 • 11-19 • 11-20 • 11-21Extreme Mode operations H11-1 • H11-2 • H11-3 • H11-4
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Main operations 12-1 • TR-22 • 12-2 • 12-3 • 12-4 • 12-5 • 12-6 • 12-7 • TR-23 • 12-8 • 12-9 • 12-10 • 12-11 • 12-12 • 12-13 • 12-14 • 12-15 • 12-16 • 12-17 • 12-18 • 12-19 • 12-20 • 12-21Extreme Mode operations H12-1 • H12-2 • H12-3 • H12-4
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Main operations 13-1 • 13-2 • 13-3 • 13-4 • 13-5 • 13-6 • TR-24 • 13-7 • 13-8 • 13-9 • 13-10 • 13-11 • 13-12 • 13-13 • 13-14 • 13-15 • 13-16 • 13-17 • 13-18 • 13-19 • 13-20 • 13-21 • 13-22Extreme Mode operations H13-1 • H13-2 • H13-3 • H13-4
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Main operations 14-1 • 14-2 • TR-25 • 14-3 • 14-4 • 14-5 • 14-6 • 14-7 • 14-8 • 14-9 • 14-10 • 14-11 • 14-12 • 14-13 • 14-14 • 14-15 • 14-16 • 14-17 • 14-18 • 14-19 • 14-20 • 14-21 • 14-22 • 14-23Extreme Mode operations H14-1 • H14-2 • H14-3 • H14-4Secret operations EG-6
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Tuning
From Episode 10 onwards, the game introduces the Main Theme Tuning system, which consists of three components: Environments, a unique milestone system, and Encourage.
Environments
Environments are essentially a "difficulty setting" for operations, allowing the player to decide how difficult the operations will be and permitting new players easier access to later Main Theme operations.
The Environment difficulty options are unlocked by clearing the previous operation' corresponding difficulty option (e.g. 10-5's Adverse Environment will only be available after 10-4's Adverse Environment is cleared first), called Environmental Compatibility and will automatically set operations to the highest difficulty setting available unless otherwise indicated. Clearing an operation in the higher difficulty retroactively counts as a clear of the lower difficulties as far as rewards are concerned (i.e. clearing Adverse Environment from the onset will also award the rewards of Standard Environment and Story Environment). However, starting by the Adverse Environment iteration of the operation will consume double the 
Sanity, as both the Sanity of the Standard Environment and Adverse Environment will be expended at once, similar to a player doing an operation's normal and Challenge Mode versions in a row.
Story Environment
An easier experience for the sake of having the story and gameplay of Arknights without some of the more difficult aspects of the game, Story Environment is intended for players who merely seek to engage with the story first, and want to leave more difficult content for a later date, or not at all.
- Friendly units are buffed significantly:
- Max HP, ATK, and DEF doubled.
- Redeployment cooldown halved.
- Only gives out the first clear rewards, but not the usual
Originite Prime. - Does not consume Sanity and no
EXP and 
LMD will be awarded (except when the operation is cleared for the first time for the latter).
- Story Environment does count towards Operator Module missions' progression.
Episode 09 operations retroactively receives Story Environment versions when Episode 10 is released; players who have already completed Episode 10 operations prior to this may access Episode 09 from the Terminal at any time to receive the rewards from the Story Environment version of the respective operations.
The previous Episodes might receive Story Environment versions at a later date, but this remains to be confirmed.
Standard Environment
Standard Environment is the normal, baseline difficulty.
Adverse Environment
Adverse Environment is functionally similar to and replaces Challenge Mode from Episode 10 onwards with the following distinctions:
- The Life Point count is no longer reduced to 1.
- Costs only one
Drill Plan for a practice run. - No longer halves the Sanity refunded upon quitting or failing, instead refunding 95% of the Sanity spent as with every other operation.
- Awards the regular, special, and extra drops when cleared, like the Standard Environment version.
- Certain operations will have completely different maps and enemies in Adverse Environment than in Story/Standard Environment instead of having handicap(s), effectively making it a different operation altogether.
Milestone
Main Theme episodes from Episode 10 features a milestone which is reached by clearing different Environment stages (if applicable) of certain operations in the corresponding episode, which gives out rewards and additional story content. The milestone is always available, thus there is no need to rush to complete them.
Encourage
For the first two weeks after a Main Theme episode is released, the Sanity consumed to run the corresponding episode's operations will be fully refunded if the player quits or fails the operation until the operation is cleared. This applies to both Standard and Adverse Environments, meaning there is no point in using any Drill Plans and the player may try the operations as many times as they wish without consequence.
Extreme Mode
From Episode 05 onwards, each episode also includes Extreme Mode operations that are added one week after the release of their corresponding episode (Episode 09, however, was released with the first half of Extreme Mode operations immediately available with the second half added in the following week), the first of which is unlocked by clearing the episode's last main operation.
Extreme Mode operations can be distinguished by the "H" prefix before the operation's episode and number (e.g. H5-1) and are considerably harder than the episode's main operations, being among some of the hardest content in the game. They do not award anything aside from an Originite Prime when cleared with 3 stars for the first time and plaques for some, and they do not have a Challenge Mode version. Completing all Extreme Mode operations of an episode will unlock a Path to Glory medal.
Since Episode 10:
- Extreme Mode operations are only available in the Adverse Environment mode and always feature handicaps as with Challenge Mode operations.
- Extreme Mode operations which feature the episode's main boss enemy generally also have the boss receive additional abilities, making the operation even more challenging.
- Clearing all Extreme Mode operations is required to obtain all of the respective episode's milestone rewards, including Operator Tokens of the episode's welfare Operator.
Nomenclatures
- With the exception of those in Episode 07 and from Episode 09 onwards, Extreme Mode operations are titled after various types of hell or hell-like realms in our world's mythology and religion.
- The Episode 05 ones are titled "Operation Inferno" which refers to the interpretation of Hell in Divine Comedy.
- The Episode 06 ones are titled "Operation Cocytus" which refers to the river of wailing in the Greek underworld.
- The Episode 08 ones are titled "Operation Erebus" which refers to a realm of darkness in the Greek underworld.
- From Episode 09, the Extreme Mode operations are titled after various figures in Greek mythology.
- H9-1 to H9-3 are titled "Operation Anemoi" which refers to the wind deities, while H9-4 to H9-6 are titled "Operation Hyades" which refers to nymph daughters of Atlas.
- The Episode 10 ones are titled "Operation Helios", after the Sun God and personification of the Sun.
- The Episode 11 ones are titled "Operation Achlys", after the goddess of mist and personification of sorrow.
- The Episode 12 ones are titled "Operation Astrape", after the goddess and personification of lightning.
- The Episode 13 ones are titled "Operation Charybdis", after the sea monster.