Here is the full list of all 42 White Day: A Labyrinth Named School achievements.
Flirt with the Girls
Head Ghost Has Nice Hair
Hee-min, Still a Growing Boy?
Dangerous Pleasure
Tired of Love
Nothing Fazes Me Now
Sincerity
Clear Hard Mode
Forgive Me
Experience Death 100 Times
Clear Normal Mode
Friendship
Experience Death 50 Times
Experience Death 10 Times
Arrive at the Bottomless Pit
Visit the Labyrinth
Arrive at the Auditorium
Arrive at the New Building
Experience Death for the First Time
Arrive at Main Building 2
I'm Perfectly Fine
You Can't Do this
Delicious Soy Milk
Enter Main Building 1
Clear Very Easy Mode
Clear Easy Mode
Clear Hell Mode
Clear Hell Mode 7 Times
Clear Hell Mode 10 Times
Truth
Hipocrisy
You Are Mine
Hidden Love
Encounter All the Ghosts in Yeondu High School
Collect All the Ghost Stories of Yeondu High School
Complete the Ghost Collection
Complete the Ending Collection
Woman living in a cabinet
Bathroom is Scary
Each Encounter is a Surprise
She Approaches from Afar
The Scent of the Bathroom is Becoming Heavenly