Overview

Babylon is an anime adaptation of a 3-volume novel. The entirety of the series is adapted into 12 episodes.
The themes of the series are presented through the dichotomy of its main characters: Zen, a Japanese prosecutor who dramatically experiences the events of the story and has his righteousness challenged until the very end, and the personification of the Christian apocalyptic myth of the Whore of Babylon, Ai. To say that these characters represent good and evil would be missing the point of the work. Despite Zen's name literally meaning "good" as in "Tree of Knowledge of Good and Evil," the accurate way to describe the relationship between Zen and Ai is that of light and dark. We know everything about Zen and we follow his adventure of pursuing justice, while Ai remains shrouded in mystery — we only see the products of the actions of this agent of chaos.

Volume 1

Episodes 1-3 introduce the city of Shiniki. On the surface, it is said to have been established to combat the effects of centralization around Tokyo, but we are then presented with the first theme of the show: corruption. We follow prosecutor Zen as he investigates a pharmaceutical company accused of bribing universities to publish false studies that would accelerate the approval of their newest drug into the market. While the story unravels around Zen finding just how deep this corruption runs — going as far as involving his own boss and seeing how powerless he is in actually delivering justice — we catch a glimpse of Ai's doings relating to this theme. She has tempted the maker of a cutting-edge euthanasia drug into taking it himself. The viewer is challenged by both Zen's side of the story and Ai's. Is it right to accelerate the adoption of drugs into the market? They could save many lives by being adopted faster, indeed. Is it right to make the maker of a suicide-assisting drug take it himself? He was convinced to do it of his own will by Ai, after all.

Volume 2

Episodes 4-7 are about legislating suicide in Shiniki. We follow Zen's prosecution of the mayor of the city for having encouraged mass suicide as a way to introduce his new project of making suicide legal. The show quietly builds on the original case of the corrupt pharmaceutical company bribing universities to publish false studies, unveiling a conspiracy to spread this legislation of suicide so they could sell their euthanasia drug — developed in secret so they could be one step ahead of the competition — around the nation. Once again, we get but a glimpse of Ai's workings, as she has infiltrated the mayor's family, hinting at the fact that she has pushed him to use Shiniki as a testing ground for the contentious law.

Volume 3

Episodes 8-12 show us that this conspiracy was not limited to Japan but intended to spread worldwide. We once again follow Zen, now an FBI investigator working for the president of the USA. Through his investigation, we are shown how Ai is actively pushing for this law to be adopted in key cities across nations that are part of the "G7" — a reference to the myth of the Whore of Babylon. After Ai manages to convince the president of the USA to kill himself, Zen is left with no other choice but to kill him so it will look like a murder instead of a suicide, which would be exactly what the cabal wanting the law adopted worldwide wants.

Ai's Special Abilities

Throughout the show, we are shown that Ai has the ability to make people want to kill themselves. It is presented theatrically but ultimately explained through Zen's journey. She tempted him into committing a murder-suicide so he could fight the conspiracy — a classic retelling of "the road to hell is paved with good intentions."
We are also shown that she has the ability to significantly alter her appearance, which is hinted to be a grotesque product of wearing her victims. This is suggested in Volume 2, where she is shown dismembering Zen's female assistant, implying she may literally don the identities of the women she kills.

Zen's Conundrum

Throughout the show, Zen is trapped in a tension between functional and moral reasoning. We are shown that he is open to being functional rather than being constrained by morality when he chooses to work with his journalist friend despite interaction between prosecutors and journalists being forbidden, when he chooses to strategically ignore arresting some politicians partaking in prostitution so that he can gather more information and have a better chance of catching the kingpins of their operations, and ultimately when he chooses to murder the president to prevent the legitimization of mass suicide. He functionally chooses the lesser harm. In this way, Ai proves he is like her, ultimately unburdened by morality.
The myth of the Whore of Babylon originates in the New Testament, written in the frame of moral reasoning and deeming it unrighteous to kill. Zen is seduced into immorality, into what is evil and wicked within that frame, through function.