On November 7, 2018, Nintendo released a new FEH Channel announcement at 7:30 Pacific Time. They detailed two new features as well as mention the arrival of Book 3.
Grails are a new form of currency that you can spend to recruit Tempest Trial and Grand Hero Battle Units. You can recruit them up to 20 times each and initially cost 100 Grails. The cost increases by 50 per summon and maxes out at 500.
Now, any hero that was obtainable previously is re-obtainable, and you'll be able to merge them up to +10. Heroes available through this feature are listed below.
- Aether Raids are a new Arena-style mechanic that will allow players to earn Grails.
- Each player will setup their own "Aether Keep" which will contain an array of buildings and four units.
- These buildings will be bought with a new currency called Aether Stones, which are also earned through completing Aether Raids.
- The buildings will provide useful buffs and debuffs during battle.
- You can destroy enemy buildings.
- Aether Raids will be completed using "Aether", which will refill weekly.
- Aether Stones and Heroic Grails are earned after a weekly reset, based on "Lift" and "Tier".
- Feature Launch: November 8, 2018
- Special structures will be available November 18, 2018
Aether Raids Rewards
Book 3 Arrives December
They also mentioned Book 3 arrives in December!