Here is the full list of all 14 Ann achievements. It takes around 2-3 hours to unlock all of the achievements on Windows.
Survived the Piano Department.
Achieved ending 1.
Triggered a disturbing event 1.
Triggered a disturbing event 2.
Survived the Sculpting Department.
Triggered a disturbing event 3.
Survived the Fashion Department.
Survived the Exhibition Hall.
Achieved ending 2.
Survived the wrath of Hana.
Achieved ending 3.
Triggered a disturbing event 4.
Achieved ending 4.
Achieved ending 5 (True Ending)