Here is the full list of all 40 Our World Is Ended achievements.
Cleared the Prologue.
Cleared Chapter 1.
Cleared Chapter 2.
Cleared Chapter 3.
Cleared Chapter 4.
Cleared Chapter 5.
Cleared Chapter 6.
Cleared Chapter 7.
Cleared Chapter 8.
Cleared Chapter 9.
Cleared the Interlude.
Cleared Chapter 10.
Cleared Chapter 11.
Cleared Chapter 12.
Cleared Chapter 13.
Cleared Chapter 14.
Cleared Chapter 15.
Cleared Chapter 16.
Got the Normal End... Hurray?
Cleared Chapter 17.
Cleared the Epilogue.
Got the Owari Ending.
Got the Iruka No.2 Ending.
Got the Asano Ending.
Got the Natsumi Ending.
Got the Tatiana Ending.
Got the Yuno Ending.
Got the Reina Ending.
Viewed all of Owari's Events.
Viewed all of Iruka's Events.
Viewed all of Asano's Events.
Viewed all of Natsumi's Events.
Viewed all of Tatiana's Events.
Viewed all of Yuno's Events.
Tried out the S.O.S. System!
You failed to choose on the S.O.S.
You failed to choose on the S.O.S. 20 Times! Yikes!
Viewed every Event CG. Nice!
Selected every branching choice. Wow!
All Achievements acquired! Good job!