Babylon manifests as a goddess dwelling within the Holy Grail artifact, discovered in Diablo's dungeon labyrinth. Visibly, she takes the form of a middle-school-aged girl, small enough to fit in the palm of Horn's hand, and wears a school uniform.

Only those who offer blood to the Holy Grail can perceive Babylon. An exception occurred when Horn, intruding into Diablo's labyrinth, urinated into the Grail instead. Babylon consumed this liquid, mistaking it for blood, forming a unique bond that now allows only Horn to see and hear her. She described the taste as unusual.

Babylon exhibits a playful, bright, and mischievous personality. She frequently teases Horn and possesses an adventurous spirit. She often withholds valuable information from him, leading to complications and positioning her more as an observer. Horn leverages his unique interaction to threaten damaging the Holy Grail, coercing her cooperation. Babylon counters these threats by claiming she will curse Horn, though her actual cursing ability remains unverified.

Functionally, Babylon serves as the mechanism powering the Holy Grail's ability to grant levels. She consumes blood offered to the grail, converting it into "Level Up" enhancements for the offerer. She also possesses an ability to sense objects capable of triggering level increases. Her involvement is specifically noted within the events of light novel volumes 6 and 10.