Here is the full list of all 40 Soulstice achievements.
Witness the first Echo
Complete Chapter 1
Obtain at least 3000 points from bonuses in a fight
Discover the first Challenge
Meet Donovan, The Shadeless
Master the Rapture state
Recover from the Berserk state
Unveil the Weavers' deception
Confront Donovan
Absorb the first crystal
Encounter Hannah
Absorb the second crystal
Reveal the last Memory
Complete the game
Complete the game on Knight difficulty
Complete the game on Chimera difficulty
Complete the game on Transcended difficulty
Upgrade Health to max level
Upgrade Entropy to max level
Complete all Challenges
Purchase all of Briar's skills
Purchase all of Lute's skills
Defeat 500 Corrupted
Defeat 500 Wraiths
Defeat 500 Possessed
Defeat more enemies than Donovan in Chapter 4
Have Lute destroy every clone of Arrowhead on her own
Prevent the Weavers from reviving each other
Find the stranger from another world
Recover more than half of your health in a fight, without using consumable items
Complete one Chapter on any difficulty, obtaining Diamond
Complete all Challenges obtaining Diamond
Complete one Chapter on Knight or higher difficulty, without being hit once
Complete game on Initiate difficulty, obtaining Platinum or above
Complete game on Knight difficulty, obtaining Platinum or above
Complete game on Chimera difficulty, obtaining Platinum or above
Defeat the Harbinger on Transcended difficulty, obtaining Diamond
Perform one Synergy attack with each weapon in the same Chapter
Perform all four Rapture finishing moves
End a fight with a Rapture finishing move