Underground (Story)

The Story Underground, which can also be referred to as PvE Underground, Underground Chapters, or simply Underground, is an important area in the game that complements the regular Chapters, unlocking at Player Level 10.
It follows a similar approach to Main Story, where players must battle predefined teams for progression, resources, Unit tokens, and other various rewards.
Over the course of the game, the player can end up spending a lot of time in the Underground so it's a very important area to master.
=Structure of the Underground=
==Chapters==
* Just like the Main Story, the Underground is split into Chapters.
* Each chapter is split into 5 chained stages that must be completed in order.
* Underground Chapters unlock in parallel with the Main Story Chapters. For example, the player must first progress to Chapter 7 in the Main Story to unlock Underground Chapter 7.
* In-between stages the user may collect . This is one of the main sources of obtaining this important and rare resource. Note that these crystals do not regenerate - each can be collected only once by the player.
* Beating all stages in a chapter with 3⭐ rewards the player with that chapter's Reward Chest. Just like for the Daily Missions, the chest must be manually clicked to obtain this one-time-only reward.
* Reward chests generally contain more , specific hero tokens, and other goodies.
==Stages==
* Each stage features a predefined team formation (Units + Hero) that can be battled by the player.
* To pass a stage the player must beat the enemy formation in manual combat.
* Fighting in a chapter costs 12. If the player wins that particular battle, all of the energy remains drained. Otherwise, the game deducts only a penalty of 1.
* Unlike regular Story Stages, each Underground Stage has a limited number of charges - number of times the player may complete the same stage. Charges reset every day or may also be manually reset by paying a specific diamond amount.
* During Life Celebration each stage gains +1 additional charge.
* After a stage has been beaten for the first time, the player can skip the manual battle by sweeping - this is the same mechanism as in the Main Story.
==Stage Rewards==
Each stage features specific unit rewards that the player will receive by repeatedly beating that level. 
* 1 Book - all stages in a chapter reward the player with a specific tier, and are always guaranteed. This is the main resource you want to farm in the Underground. 
* 1 - this is also always granted by beating a level, and is required to level up a Hero's spells. This is an incidental reward and not something the players would actively farm in the Underground.
* Secondary reward - just like the enemy formation, each stage also has a predefined (hardcoded) secondary reward. It drops often, but not every time the stage is beaten. Even so, these rewards are also rather difficult to farm efficiently in other places and therefore can determine the specific stage the player will opt to sweep. 
** Unit token - this allows players to farm and increase the rank of specific units they are building for their formation. Note that clearing a stage does not guarantee a token award.
** Equipment resources - these only appear in the early stages and are not worth farming in the Underground, as Main Story stages are cheaper to sweep.
** 1 Book - unlike the guaranteed book, however, this is always 1 tier lower.
** Spell tokens - these appear only in later stages and can be used to either unlock spells in the Spell Bookshelf or dismantle for (which can in turn be used to purchase specific spells in the Spell Store).
** During Steadwick Incident Defence Stage, each Underground stage can also drop Legendary, Expert, and Basic Building Materials used to upgrade Steadwick's Walls. After the Steadwick Incident Defence stage ends, they will never drop again.
* Awakening Soul Tokens - active only while the third Awakening Mission is in progress. It replaces the secondary reward but one token is always guaranteed by beating the stage.
=Chapters=
==Chapter 1 - Homecoming==
Minimum Level: 10
Claimable Crystals: NA
Main rewards:
				
Chapter Chest reward: 200, 10K, 5, 15x Catherine Tokens
==Chapter 2 - Guardian Angel==
Minimum Level: 10
Claimable Crystals: NA
Main rewards:
				
Chapter Chest reward: 200, 20K, 5, 15x Catherine Tokens
==Chapter 3 - Griffin Cliffs==
Minimum Level: 10
Claimable Crystals: NA
Main rewards:
				
Chapter Chest reward: 250, 20K, 5, 15x Catherine Tokens
==Chapter 4 - A Devilish Plan==
Minimum Level: 10
Claimable Crystals: NA
Main rewards:
				
Chapter Chest reward: 250, 30K, 60, x15 Catherine Tokens
==Chapter 5 - Pioneer==
Minimum Level: 10
Claimable Crystals: 150
Main rewards:
				
Chapter Chest reward: 300, 30K, 70, x15 Catherine Tokens
==Chapter 6 - Fall of the Capital==
Minimum Level: 10
Claimable Crystals: 150
Main rewards:
				
Chapter Chest reward: 300, 50K, 80, x15 Rashka Tokens
==Chapter 7 - Borderlands==
Minimum Level: 10
Claimable Crystals: 150
Main rewards:
				
Chapter Chest reward: 350, 50K, 90, x15 Rashka Tokens
==Chapter 8 - Frenzied Thoughts==
Minimum Level: 32
Claimable Crystals: 150
Main rewards:
				
Chapter Chest reward: 350, 50K, 100, x15 Rashka Tokens
==Chapter 9 - Greed==
Minimum Level: 35
Claimable Crystals: 150
Main rewards:
				
Chapter Chest reward: 400, 80K, 110, x15 Rashka Tokens
==Chapter 10 - Gryphonheart==
Minimum Level: 38
Claimable Crystals: 150
Main rewards:
				
Chapter Chest reward: 400, 80K, 120, x15 Crag Hack Tokens
==Chapter 11 - Harvest Season==
Minimum Level: 41
Claimable Crystals: 150
Main rewards:
				
Chapter Chest reward: 450, 80K, 130, x15 Crag Hack Tokens
==Chapter 12 - Corporal Punishment==
Minimum Level: 44
Claimable Crystals: 150
Main rewards:
				
Chapter Chest reward: 450, 100K, 140, x15 Crag Hack Tokens
==Chapter 13 - From Day to Night==
Minimum Level: 48
Claimable Crystals: 150
Main rewards:
				
Chapter Chest reward: 500, 100K, 150, x15 Crag Hack Tokens
==Chapter 14 - Safe Passage==
Minimum Level: 52
Claimable Crystals: 150
Main rewards:
				
Chapter Chest reward: 500, 100K, 160, x15 Shiva Tokens
==Chapter 15 - United Front==
Minimum Level: 56
Claimable Crystals: 150
Main rewards:
				
Chapter Chest reward: 500, 100K, 160, x15 Shiva Tokens
==Chapter 16 - For King and Country==
Minimum Level: 60
Claimable Crystals: 150
Main rewards:
				
Chapter Chest reward: 500, 100K, 160, x15 Shiva Tokens
==Chapter 17 - Liberation of the Empire==
Minimum Level: 64
Claimable Crystals: 150
Main rewards:
				
Chapter Chest reward: 500, 100K, 160, x15 Shiva Tokens
==Chapter 18 - Deal with the Devil==
Minimum Level: 68
Claimable Crystals: 150
Main rewards:
				
Chapter Chest reward: 500, 100K, 160, x15 Mephala Tokens
==Chapter 19 - Neutral Ground==
Minimum Level: 72
Claimable Crystals: 150
Main rewards:
				
Chapter Chest reward: 500, 100K, 160, x15 Mephala Tokens
==Chapter 20 - Tunnels and Troglodytes==
Minimum Level: 76
Claimable Crystals: 150
Main rewards:
				
Chapter Chest reward: 500, 100K, 160, x15 Mephala Tokens
==Chapter 21 - The Grail==
Minimum Level: 80
Claimable Crystals: 150
Main rewards:
				
Chapter Chest reward: 500, 100K, 160, x15 Mephala Tokens
==Chapter 22 - The Road Home==
Minimum Level: 84
Claimable Crystals: 150
Main rewards:
				
Chapter Chest reward: 500, 100K, 160, x15 Yog Tokens
==Chapter 23 - Independence==
Minimum Level: 88
Claimable Crystals: 150
Main rewards:
				
Chapter Chest reward: 500, 100K, 160, x15 Yog Tokens
==Chapter 24 - Elemental Tide==
Minimum Level: 92
Claimable Crystals: 150
Main rewards:
				
Chapter Chest reward: 500, 100K, 160, x15 Yog Tokens