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