This achievement is unlocked when you view A2's achievement for the first time. It can be achieved on your third playthrough or later using the chapter select feature that becomes available upon completion of the third playthrough.
The earliest this achievement can be unlocked is during your third playthrough. Towards the end of the third playthrough, you will activate the main story mission "To the Top." You will alternate between controlling A2 and 9S. Eventually, the two characters will meet. To unlock this achievement choose to play A2. You will view A2's ending and unlock the achievement.
If you choose to play as 9S, you will not unlock this achievement in your third playthrough. Instead, you will get 9S's ending and unlock the following achievement:
This is perfectly acceptable. If you elect to pursue this approach, when you are ready to get A2's ending and, with it, this achievement; from the title screen load any save file made after your third playthrough. Go to chapter select and load Chapter 17-09. This time, select A2 as your playable character. You will then achieve A2's ending, the C ending.
If you abort, the achievement will unlock when you abort. If you choose to continue play by answering Yes to the pod's question following the credits, this achievement will unlock along with The Minds that Emerged achievement for the E ending. The achievements unlock at the black screen following the E ending cut scene. Recommendation
: Because there are two variants of 9S's ending and only one of A2's ending, I recommend doing one variant of 9S's ending in the third playthrough (thereby deferring this achievement to later) and using chapter select later to get A2's ending (and with it this achievement) followed by the second variant of 9S's ending. The differences are very minor. Moreover, from an achievement standpoint, you are only required to view one variant of the D ending. So, you are free to pursue your personal preferences. The following guide provides No Spoiler analysis of some of the finer points regarding the unlocking of the achievements associated with the game's fourth and fifth endings: Solution for The Minds That Emerged in NieR: Automata BECOME AS GODS Edition
If the achievement does not unlock after achieving A2's ending for the first time, you have probably experienced a glitch. In the event of a glitch, clear the cache. To do so, turn off the console by holding the
button on the console for at least ten seconds and then unplug the console for at least 20 seconds. Load any save made following the third playthrough and use the chapter select feature and load chapter 17-09. Clearing the cache will most likely remedy the problem and the achievement should unlock when you select A2 and see her ending. Note that, if you already have the D ending and choose to continue play as discussed above, the achievement unlocks at the black screen following the E ending cut scene.