Here is the full list of all 71 Prime of Flames achievements.
Defeat Queen Beelica
Defeat Warden
Defeat Iron Champion
Defeat Evision
Defeat Draserpent
Defeat Mudtain
Defeat Frostfang
Defeat Winter General
Defeat Crossbow Brothers
Defeat Despairer
Defeat Condemner
Defeat Crystalforger
Defeat Bladehand
Defeat Watcher
Defeat Ursa
Defeat Blood Chief
Defeat Bonfire Knight
Defeat Aerolistar
Defeat North Wind
Defeat Sin Eater
Defeat Eternal Guard
Defeat Karma
Defeat Batragon
Defeat Heart Colossus
Defeat Deaterfly
Defeat Azure Centaur
Defeat Oracle
Defeat Yama
Defeat Sigma
Deal 100+ Damages in one Attack
More than 5 Ninelie Cavalries in your team when you clear the Chapter
More than 3 Colossi in your team when you clear the Chapter
More than 5 Warriors in your team when you clear the Chapter
More than 5 Guards in your team when you clear the Chapter
More than 5 Scouts in your team when you clear the Chapter
More than 5 Hunters in your team when you clear the Chapter
More than 5 Priests in your team when you clear the Chapter
No character is killed when you clear the Chapter
You have more than 2000 Coins when you clear the Chapter
Clear Chapter VI with Ninelie
Clear Chapter VI with Bronion
Clear Chapter VI with Evernight
Save Queen Beelica from Wudie control
Get Iron Champion drunk and have a good sleep
Guide the soul of Crystalforger to rest
Let Watchers regain their consciousness
Help Frostfang guard Wolf Priestess
Go to the North to scare away the Acient Dragon named North Wind
Help Eternal Guard retrieve his memory
Attack Wudie Camp with Azure Centaur together
Pass the special test of Karma
Clear 5 Stages in Endless Mode with any Clan
Clear 10 Stages in Endless Mode with any Clan
Clear 20 Stages in Endless Mode with any Clan
Clear 30 Stages in Endless Mode with any Clan
Clear 50 Stages in Endless Mode with any Clan
Clear 80 Stages in Endless Mode with any Clan
Clear 100 Stages in Endless Mode with any Clan
Clear the BOSS stage without any damage
Clear the BOSS stage with only one character
Clear the stage in one turn
Kill more than 5 enemies in one attack
Revive more than 5 characters at a time
Unlock all the characters in Illustrated Book
Start your Journey at the first time
Unlock all the spots in single Journey
Consume 200 Prayer Stones in total
Consume 500 Blood Crystals in total
Consume 10000 Coins in total
Defeat the gods with the help of the crowd
Defeat the gods with the power of Venus