Did 2B kill multiple 9S units before the 9S model we played? I was a little confused with what A2 revealed about 2B at the end.
If 2B did kill multiple 9S units before actually sparing 9S, then that is a very interesting foil between 9S self-made mission to kill all machines versus 2B's reluctance to kill our 9S.
Also interesting is that 9S ignored 2B's compassion for 9S units til the very end. A lot of layers for Android/machine racism here unless I'm overthinking it.
9s is the same model, the same "person" to some degree and yes she has killed him quite a bit.
basically 2b and 9s have been paired for a long time, and 9s is so valuable to the war effort that it's worth keeping him around despite his inevitability in discovering the truth behind the yorha project (that humanity is dead and they are effectively decoys for allowing androids to fight a pointless eternal war)
the thing is that, every time 9s comes close to discovering this 2b is ordered to kill him and then reset his memories so he doesn't remember anything- so a brand new 9s pops out with no memories of their time together.
the revelation of 2E, is specifically the model type "E" is built for the purpose of going undercover and assassinating androids who are detrimental to the war effort- there's a sidequest that deals with this called "amnesia".
as androids are effectively all-but-human in how they function and act, it's no surprise this is mentally straining and causes the android in that quest so wipe her memories because she simply cannot handle the stress of becoming close friends with people she is built to kill anymore.
here's the kicker:
9s loves 2b, somewhat due to residual memories and a general sense of familiarity due to how much time they've spent together despite his memory wipes. you can see this in his usage of the "nines" nickname, which is very clearly something that 2b came up with during one of his past 'lives'
2b loves 9s for who he is, but is forced to kill him over and over again because it is her duty to do so. and in doing so, he is always forgetting the experiences and times they've shared together, good or bad- her being upset that 9s didn't remember sacrificing himself to save 2b in terms of uploading her memory first in the prologue or their mutual suicide is just one of hundreds, if not thousands of examples of things that make her just love him more.
to note, 2b already knows the secret of the yorha project and is willingly fighting in an unwinnable war just so that she can be close to 9s- if you take note of the virtuous contract and cruel blood oath's weapon stories, they're actually very blatantly about her relationship with 9s.
the way she interacts with 9s is a constant battle between her wanting him to be closer to her and the emotional need to keep him distant enough so when it comes time to kill him, she can actually perform the deed as she remembers every single time she's done it.
Cruel Blood Oath said:
Level 1
I'll never forget the time we met. I knew ours was a love that would last for eternity."
Level 2
But even when by his side, his feelings were a mystery. It was painful not to know what he was thinking. So painful."
Level 3
When I was close, I hurt him. Yet being distant hurt him more."
Level 4
I finally found my place in life. A place where I am as close as possible, yet eternally distant."