Ai Magase stands as the central antagonist throughout the Babylon narrative. Her origins remain largely undefined, though fragmented accounts describe her adoption at age seven by Kurauzu Sakabe's brother, after which she displayed disturbing behavioral tendencies. By fifteen, she exhibited abilities to psychologically traumatize individuals through undefined seductive qualities, reportedly causing seven middle school boys to require counseling after experiencing sensations described as figurative "rape" despite no physical contact. Sakabe documented overwhelming arousal during her counseling sessions, forcing him to close his clinic and relocate to avoid acting on impulses attributed to her influence.

Her abilities include physically altering her appearance to assume different identities—varying significantly in height, facial structure, and body shape—with no known biological limitations, enabling her to infiltrate social and political circles undetected. Her most distinctive capability involves inducing psychological states that drive individuals to suicide or compliance through vocal modulation, presence, or implied sexual allure. This influence manifests as an overwhelming aura of "eroticness" creating hallucinations in targets, effective even through auditory channels like telephone communication. Affected individuals experience sensations described as ecstatic compulsion preceding self-destructive acts.

Within the story, she strategically manipulates political figures involved in the Shiniki autonomous city initiative. Her early manipulations target individuals connected to pharmaceutical corruption, including anesthetist Shin Inaba—whom she seduces prior to his ecstasy-fueled suicide—and prosecutor Atsuhiko Fumio, whom she similarly drives to self-destruction during an investigation. Later, she assumes identities like Emiko Hiramatsu and Kanae Kuyou to bypass interrogation and infiltrate higher power levels. Her pivotal manipulation compels mayoral candidate Kaika Itsuki to propose radical legislation legalizing suicide across Shiniki, culminating in a mass suicide event where Itsuki and followers leap from a building as Magase observes.

Her methodology extends into philosophical manipulation. She engages characters like prosecutor Zen Seizaki in discussions framing evil as a necessary counterpart to good, claiming her actions originate from a desire to become a "hero" who saves people by embracing darkness. During the torture and decapitation of Seizaki's assistant Sekuro, she articulates a worldview where evil holds intrinsic meaning, positioning herself as an inevitable force mirroring humanity's hidden desires.

Symbolic interpretations associate her with the Whore of Babylon, particularly through her capacity to psychologically intoxicate powerful figures and nations. Additional references frame her as a metaphysical representation of temptation or primordial evil, likened by some characters to the serpent in the Garden of Eden. This thematic connection underscores her role in corrupting systems and individuals psychologically, though narrative ambiguity leaves precise interpretation unresolved.

Her actions escalate globally after Shiniki's collapse, including the assassination of the U.S. President and manipulation of international figures during a United Nations summit. Her final confrontation with Seizaki ends inconclusively, leaving her as an unresolved existential threat.