| Event | Rerun | Synopsis | OST | Gallery | Trivia |
Heart of Surging Flame is the second major event and Side Story in Arknights.
The event is divided into three parts in the Global server.
Operators
Headhunting
- Main article: Headhunting/Banners/Former/2020
The Forging Steel headhunting banner is featured.
Obsidian Festival Bracelet
Collect 
Obsidian Festival Bracelet to claim the following rewards by completing Daily and Event Missions.
300 
|
 3 |
| 600
|
 5 |
| 900
|
 40 |
| 1200
|
|
| 1500
|
 200 |
| 1800
|
 2 |
| 2100
|
 30 |
| 2400
|
 25 |
| 2700
|
 5 |
| 3000
|
2 |
| 3300
|
|
| 3600
|
 30K |
| 3900
|
 1 |
| 4200
|
 1 |
| 4500
|
 |
Each excess Obsidian Festival Bracelet will be converted into 20 
(given as an in-game mail) at the end of the event.
Missions
Daily
During the event, the rewards for Daily Missions are changed to the following:
| #0 | 500 |
|---|---|
| #1 |  3 |
| #2 | 1K  2 |
| #3 |  40 |
| #4 | 1 5 |
| #5 | 2K  3 |
| #6 | 50 |
| #7 |  1  5 |
| #8 |  100 |
| #9 |  5 600 |
| #10 | 60 |
Event
| Mission | Reward |
|---|---|
Spend a total of 800 
|
50 |
| Spend a total of 1600
|
100 |
| Spend a total of 2400
|
150 |
| Gain a total of 50000 Operator EXP through training | 50 |
| Gain a total of 100000 Operator EXP through training | 100 |
| Gain a total of 150000 Operator EXP through training | 150 |
| Spend a total of 80000 to train or promote Operators
|
50 |
| Spend a total of 160000 to train or promote Operators
|
100 |
| Spend a total of 240000 to train or promote Operators
|
150 |
Spend a total of 1000  at the Credit Store
|
50 |
| Spend a total of 2000 at the Credit Store
|
100 |
| Spend a total of 3000 at the Credit Store
|
150 |
| Send 6 Clues to friends | 50 |
| Send 12 Clues to friends | 100 |
| Send 18 Clues to friends | 150 |
| Defeat a total of 1000 enemies in Annihilation stages | 50 |
| Defeat a total of 2000 enemies in Annihilation stages | 100 |
| Defeat a total of 3000 enemies in Annihilation stages | 150 |
| Clear any stage a total of 40 times | 50 |
| Clear any stage a total of 80 times | 100 |
| Clear any stage a total of 120 times | 150 |
| Defeat a total of 3000 enemies | 50 |
| Defeat a total of 6000 enemies | 100 |
| Defeat a total of 10000 enemies | 150 |
| Use Recruitment 10 times in total | 50 |
| Use Recruitment 25 times in total | 100 |
| Use Recruitment 40 times in total | 150 |
| Assign 100 Operators to restore Morale in the Dormitory | 50 |
| Assign 200 Operators to restore Morale in the Dormitory | 100 |
| Assign 300 Operators to restore Morale in the Dormitory | 150 |
| Complete 50 orders | 50 |
| Complete 100 orders | 100 |
| Complete 150 orders | 150 |
| Produce 100 Pure Gold in the Factory | 50 |
| Produce 200 Pure Gold in the Factory | 100 |
| Produce 300 Pure Gold in the Factory | 150 |
| Conduct 1 Clue Exchange | 50 |
| Conduct 2 Clue Exchanges | 100 |
| Conduct 3 Clue Exchanges | 150 |
Operations
Clear 1-10 to access OF operations.
| Main Stage | OF-ST1 • OF-1 • OF-ST2 • OF-2 • OF-3 • OF-4 • OF-ST3 • OF-5 • OF-6 • OF-ST4 • OF-7 • OF-8 • OF-ST5 |
|---|---|
| Fairground | OF-F1 • OF-F2 • OF-F3 • OF-F4 |
| Extra Show | OF-EX1 • OF-EX2 • OF-EX3 • OF-EX4 • OF-EX5 • OF-EX6 |
Extra Show operations are available in the second week of Part 2.
All OF operations are worth 29 
.
Operators
Ceylon is awarded when OF-4 is cleared for the first time.
The following Operators gain 50% extra Trust (except from Annihilation):
Headhunting
- Main article: Headhunting/Banners/Former/2020
The Summer Guardians headhunting banner is featured.
Band choices
When entering the event menu for the first time, after watching the Obsidian Festival intro, the player must choose one of the three musical acts listed below, with the choice being permanent for the rest of the event.
The choice will affect the special furniture given by completing the Siesta Obsidian Milestone and the music heard in the OF menu.
| Musical act | Genre | Menu theme | Milestone reward |
|---|---|---|---|
|
Heavy metal |  | |
|
EDM |  | |
|
Hip hop |  |
Band Trends
Upon choosing a particular band, there wil be a small window featuring trends concerning them.
- For more information, see Heavy Metal Trend, EDM Trend, and Rap Trend.
Collectibles
Siesta Obsidian
Siesta Obsidian are awarded from clearing Main Stage operations and completing Daily Missions.
Rewards will be given once the player accumulated a certain threshold of Siesta Obsidians in the Siesta Obsidian Milestone.
Obsidian Festival Ticket
Obsidian Festival Ticket are awarded from clearing Main Stage operations, completing Daily Missions, and the Siesta Obsidian Milestone.
Obsidian Festival Tickets are used to run Fairground operations, which awards Obsidian Festival Token.
Obsidian Festival Token
Obsidian Festival Token are awarded from clearing Extra Show operations for the first time, completing Daily Missions, and the Siesta Obsidian Milestone.
Obsidian Festival Tokens are used for the Capsule Machines.
Siesta Obsidian Milestone
The Siesta Obsidian Milestone rewards can be claimed until March 20, 2020.
50 
|
10K |
| 100
|
10 |
| 150
|
5 |
| 200
|
 6 |
| 250
|
 60 |
| 300
|
15K |
| 350
|
20 |
| 400
|
 |
| 450
|
 300 |
| 500
|
 6 |
| 550
|
70 |
| 600
|
|
| 650
|
30 |
| 700
|
 |
| 750
|
80 |
| 800
|
5 |
| 850
|
300 |
| 900
|
6 |
| 950
|
80 |
| 1000
|
20K |
| 1050
|
40 |
| 1100
|
6 |
| 1150
|
 |
| 1200
|
90 |
| 1250
|
300 |
| 1300
|
 |
| 1350
|
25K |
| 1400
|
80 |
| 1450
|
 2 |
| 1500
|
8 |
| 1550
|
8 |
| 1600
|
300 |
| 1680
|
100 |
| 1760
|
10 |
| 1840
|
 40 |
| 1920
|
10 |
| 2000
|
|
| 2080
|
 2 |
| 2160
|
30K |
| 2240
|
40 |
| 2320
|
10 |
| 2400
|
 |
| 2480
|
 5 |
| 2560
|
 2 |
| 2640
|
100 |
| 2720
|
10 |
| 2800
|
300 |
| 2880
|
120 |
| 2960
|
|
| 3040
|
 |
| 3120
|
35K |
| 3200
|
5 |
| 3280
|
 |
| 3360
|
120 |
| 3440
|
20 |
| 3520
|
 1 |
| 3600
|
300 |
| 3680
|
 1 |
| 3760
|
 |
| 3840
|
20 |
| 3920
|
 1 |
| 4000
|
See Band choices |
Outfits
The following outfits are available in the Outfit Store:
| New |
|---|
Furnitures
Two furniture sets: Rhodes Island Modern Music Rehearsal Room and Siesta Beach Hut, are available:
- Some parts for Rhodes Island Music Rehearsal Room are obtained by clearing OF operations and from Capsule Machines and Siesta Obsidian Milestone, while most are available in the Furniture Store.
- Siesta Beach Hut is available exclusively in the Furniture Store.
Login Event
During the event, login to the game to claim the following rewards.
| Day 1 | 2 | ||
|---|---|---|---|
| Day 2 | 30K 30 | ||
| Day 3 | 5 300 | ||
| Day 4 | 5 5 | ||
| Day 5 |  2 | ||
| Day 6 | 1  1 | ||
| Day 7 |
|
Operators
From May 20, 2020:
- Ethan and Breeze replaces Cuora and FEater, respectively, as the Operators purchasable in the Shop Vouchers Store.
- Dur-nar is available on the Credit Store (in a similar way to Courier and Gavial).
Headhunting
- Main article: Headhunting/Banners/Former/2020
The Dancing Lava headhunting banner is featured.