[Suzerain of Sheol]

I actually took it a little differently.

The fact that she was crying when she had to kill 9S, and the pain in her voice when she said that line, I think she really legitimately LOVES him, even though she's not supposed to be able to feel that. And every little bonding moment they have is incredibly painful for her, because she knows it can't last, and she can't ever let anything grow between them because if she does, it'll make killing him that much harder, or even impossible.

It's an incredibly sad story, since in this horrible world they're in, where suicide is often preferable to living, a bond like that is beyond precious, and the thought that they could actually be happy together despite all the awful things that have happened to the world, if not for the pointless war they're stuck in... it's heartbreaking.

It seems to be implied that her memories are completely intact of all the time she's spent with him. I think the stoic dedication to their mission that she shows most of the time is her coping mechanism to deal with the unbelievable pain and guilt she's carrying around inside. She knows that even though their Gods (humanity) are dead, it's still possible somehow for her to have a meaningful life because of the feelings she has for 9S, but she can never have that because of the brutal reality she exists in.

And then to see the horrible anguish of her last moments, when she realizes that she's going to die for real, and that she'll never ever be able to see that dream come true, it was so powerful and sad for me. Absolutely beautiful and tragic.

A lot of the reviews and discussions I've read online say she's boring character with no depth, and I really think that's not a fair analysis of her character. You have to read between the lines and let the things you learn about her after she dies color what you saw of her when she was alive. Such a wonderful, depressing character arc.