To unlock this achievement, you have to enter "CG MODE" section after you have viewed all of the event images of this game. Choose EXTRA -> CG MODE from title menu to enter CG MODE.
To view all images, you have to do two things.
1. Complete the game with all 4 endings according to the following guides.
Solution for なべて世は事もなく In No Fate! Only the Power of Will (Mabel route complete)
Solution for 今年もよろしく In No Fate! Only the Power of Will (Kisaki route complete)
Solution for 毎日が特別な日々 In No Fate! Only the Power of Will (Rise route complete)
Solution for 僕たちの暮らす惑星（ほし） In No Fate! Only the Power of Will (Junko route complete)
2. Get a special image for bad-ending. Load one of the save data made on 11/22 as shown in the guides above. Then make the opposite choice from that of the guide (so if you've picked up Rise route data, select 1 / 2, otherwise select 2 / 2). If you picked the right choice for bad-ending, the game soon shows the date as "??.??*???????". Skip until the game is over, then select YES to the confirm.
(You have to do this for any one of the 4 routes, no need to do this for all 4 routes.)
After you've done these 2 steps, you should have viewed all the images. Enter CG MODE to get this achievement.
Should the percentage shown in CG MODE is not 100%, the achievement won't unlock. Probably you've picked a wrong choice somewhere in step 1, so repeat step 1 to view all images.