corruption

A character is somehow influenced or altered in some way from their original self to embrace a more evil and/or perverted persona. This transformation can affect their body, mind, or soul, and is often driven by an external force—such as dark magic, alien influence, parasitic control, or advanced technology. The corrupted version typically reflects a loss of humanity, morality, or autonomy, and may appear seductive, monstrous, mechanical, or utterly inhuman.

Corruption can be subtle or extreme, and may involve changes to appearance, behavior, or allegiance. The corrupted form represents a darker mirror of the original character—either as a result of internal temptation or external domination. In extreme cases, even their very body is affected as well and results in a physical transformation, which is often visualized as a physical manifestation of the corruption visibly spreading on their body until they're fully engulfed and changed.

Visual cues

As a visual cue artists will often change the character's taste in fashion, hairstyle, lifestyle, and demeanor to be more on the darker side of things such as:

A different color palette (darker or muted).
Mutated or otherwise changed body part (e.g. cybernetic limbs, bug-like broodmare abdomen, genitalia changed into ovipositor, additional parts like tentacles, etc.)
Skimpier clothes, often invoking a gothic or BDSM aesthetic.
Loss of morals and inhibitions.
A meaner personality (more aggressive, cruel, or depraved).
A tendency to do evil deeds or corrupt acts (eg. spreading corruption, growing hive).