Here is the full list of all 31 Fatal Twelve achievements.
Select every choice at least once.
Get bad ending 1
Get all endings
Get all CGs
View a story about a certain encounter
Get bad ending 4
Get ending 1
Reply to the confession
Twelfth week's election concludes
Get bad ending 3
Get bad ending 2
Open Summary Mode
Open Scene Replay Mode
Open Gallery Mode
Get ending 2
Get ending 3
Tenth week's election concludes
Eleventh week's election concludes
Ninth week's election concludes
Seventh week's election concludes
Sixth week's election concludes
Fifth week's election concludes
Fourth week's election concludes
Start the game 12 times
Open Card Book Mode
Third week's election concludes
Second week's election concludes
First week's election concludes
Switch languages
Start the game
Eighth week's election concludes