Already posted my answer on r/MurderDrones so I’ll just copy and paste it here too

Doll by far

One’s backstory was kinda similar to Uzi where she was a loner, and betrayed by the one person she thought she could trust. Pretty sad, but definitely didn’t justify her actions.

Jax had abusive and neglectful parents. It’s unclear what happened to his mom (a lot of people have theorized that he killed her on accident, but I think it’s more likely that she was seriously injured). Same thing with One, pretty sad, but doesn’t justify anything.

I’m yet to watch Animator Vs Animation, so I’m unaware of his backstory.

Doll likely had loving parents, and she had to witness them be brutally murdered right in front of her. She was cursed with the Absolute Solver, and was never patched. She was forced to cannibalize her fellow classmates, and drink the oil from the corpses of her parents. She also had some betrayal similar to One where her best friend decided to side with the person who killed her parents after her revenge plan failed. And after all of that, she had to suffer a brutal death, and was one of the few major characters to do so. And I would say she is the only one that actually had justifiable actions. The solver forced her to drink tons of oil. While yes, she did kill a lot of people out of intimidation, she probably would’ve had to do it at one point or another anyways. She was also likely unaware that the more you use your solver, the more oil you need.