Here is the full list of all 27 How to Take Off Your Mask achievements.
You've unlocked all of the Achievements!
You've unlocked all of the Movies.
You've unlocked all of the CGs.
You've unlocked all of the Music tracks.
You've cleared the Prologue!
Transformed into a luccretia for the first time!
You've cleared Bonus★Luccretia Side 1!
You've cleared the "Secret Discussion"!
You've got the Luccretia Side Ending!
You've cleared Chapter 6★Luccretia Side!
Listen to what I actually feel...
You've cleared Chapter 5★Luccretia Side!
You've cleared Chapter 4★Luccretia Side!
You've cleared Bonus★Luccretia Side 3!
You've cleared Bonus★Luccretia Side 2!
You've got the Human Side Ending!
You've cleared Chapter 6★Human Side!
You've cleared Chapter 5★Human Side!
Let me take off this "Big Sister" mask...
You've cleared Chapter 4★Human Side!
You've cleared Chapter 4
You've cleared Bonus★Human Side 3!
You've cleared Chapter 3
You've cleared Bonus★Human Side 2!
You've cleared Chapter 2
You've cleared Bonus★Human Side 1!
You've cleared Chapter 1