Here is the full list of all 40 Ninja Soul achievements.
Equip 6 level 6 items
Equip a cursed item
Your First Rewind
Spend Souls on Talent
Extract Attribute Fragement
Try Attributes Replacement with Priest
Convert an item into Coins
Acquired all Blessings of War
Acquired all Blessings of Crafter
Mastered all talents
Complete speed run once
Complete Mugen Phantom once
Complete any timeline within 20 minutes
Spend Soul Points in making Wish
Lose more than 500 Souls upon death
Any Attribute reach over 700%
Beat the game after two redemptions
Timeline I completed
Timeline II completed
Timeline III completed
Timeline IV completed
Timeline V completed
Timeline VI completed
Complete an equipment fusion
Complete a fusion with 6 different types of items
Complete a fusion with 6 different types of level 6 items
Devil's Soul Decimated
Acquire a Story Fragment
Acquire all Story Fragment
Defeat the Relentless
Defeat the Twin Iron
Defeat the Abyssal Lord
Defeat Azrael
Beat the level with a cursed item
Complete a fusion with cursed items
Killed by traps
Perform IISen twice within 5 seconds
Deal over 20000 Physical dmg within 3 seconds
Deal over 20000 Ninjutsu dmg within 3 seconds
Deal over 20000 Ranged dmg within 3 seconds