Veteran players of the NieR franchise are well aware of all the hidden lore Yoko Taro likes to put in his stories. Not only is it a fun side activity to look for things, but also it expands the world inside the game itself.
Whether it's the YoRHa androids or the Resistance, they're all part of what makes the game so lively; their personalities, goals, occasional bickering, and so on. There's even a side quest where one android gets in a predicament with her boyfriend, and it's the player's job to play the role of the couple's counselor.
Laundry Day
In real life, most of us have a designated day when we do our laundry. And in cases where a large group of people live together, sometimes it's all at once. In one of the accessible archives, a notice sent out by the higher-ups states that clothing issued by YoRHa need to be turned in for washing. It then specifies that during that time, the androids will wear civilian clothing during the day. It's a funny secret for players to find and really brings to life our favorite YoRHa soldiers. Just imagine 2B and 9S in hoodies.
The Perfect Present(?)
Early on in the game, 9S and 2B discuss what they'll both do after the war is over. One of the suggestions is casual shopping and buying clothes. 2B doesn't indict much interest, but 9S promises to buy her a T-shirt. Imagine in a battle sequence, 9S thinks of his "promise" to 2B and gets back up on his feet. Bonus points if he pictures her in one that matches his. Maybe they'll bring back couple shirts in the far future.
Nicknames Are For Friends
While 2B and 9S are on one of their excursions, 9S says in passing that his friends call him "Nines" as a nickname. 2B initially brushes him off, but later on she refers to him as such. 9S is ecstatic at her doing so - but she insists that he simply misheard her. Imagine this scene but with more facial expressions, and maybe one of their pods comforts 9S in his supposed "rejection", while the other tries to analyze what 9S was trying to convey. Or alternatively, they state that nicknames are a "human" thing, further emphasizing one of the themes of being conformative in NieR Automata's narrative.
Ex Drama
As stated above, there is a side quest given by a pair of NPCs in the overworld, who need new parts to repair themselves, after eloping and fleeing from the Resistance, though they frequently argue. They task the player to retrieve new parts, so they can continue on their journey. After being betrayed by another person who was supposed to help the couple escape, 2B and 9S once again agree to assist in the matter, repairing the female android after sustaining more damage.
Once the couple are reunited, the female android suggests getting reformatted, so they don't have to deal with the pain of being betrayed. 9S agrees to it and reformats the male android first. But before he can get to the other one, she says that there's no need. We find out that she wanted to get him reformatted, so she could "adjust" his personality more to her liking, before telling the player that this isn't the first time she's done this. What starts off as helping a couple run away together, became a mission for a girlfriend to "change" her boyfriend again to her liking. Needless to say, this has some pretty dark implications about a manipulative relationship. It would be interesting to see, however, this be explored further in the anime and potentially become a large part of 2B and 9S's character developments.