Here is the full list of all 33 SoulSet achievements.
Unlocked Mariko's True Ending
Unlocked The Secret Ending
Unlocked Feathor's True Ending
Unlocked Marco's True Ending
Unlocked Feathor's Bad Ending A
Found all the Red Clues
Unlocked Feathor's Normal Ending
Unlocked Shirr's Normal Ending
Unlocked Shirr's True Ending
Unlocked Shirr's Bad Ending A
Found all the Silver Clues
Unlocked Shirr's Bad Ending B
Found all the Green Clues
Unlocked Verin's Bad Ending A
Unlocked Verin's Normal Ending
Unlocked Verin's True Ending
Unlocked Shira's Bad Ending A
Found all the Orange Clues
Unlocked Shira's Bad Ending B
Unlocked Shira's Normal Ending
Unlocked Shira's True Ending
Read the whole thing!
Unlocked Apris' Bad Ending C
Unlocked Apris' Bad Ending B
Unlocked Apris' Bad Ending A
Unlocked Apris' Normal Ending
Unlocked Apris' True Ending
Unlocked Yvonne's Bad Ending A
Unlocked Yvonne's Normal Ending
Unlocked Yvonne's True Ending
Was he in there all along?
Unlocked Marco's Bad Ending A
Choose wisely, My Liege