Dark Rouge emerges as Cure Rouge's dark counterpart, crafted by the villain Shadow within the Mirror Kingdom. She embodies Rin Natsuki's past perspective, viewing friends and companions as inconvenient burdens. Her personality radiates extreme arrogance and wrath, standing in stark opposition to Cure Rouge's passion and loyalty. In confrontations, Dark Rouge openly mocks Cure Rouge's value of friendship, insisting that operating alone represents a superior and more efficient path.

Her combat abilities mirror Cure Rouge's fire-based powers. Her signature attack, Darkness Fire, involves firing red laser bullets from her palms, a direct counterpoint to Cure Rouge's Rouge Burning. When battling Cure Rouge, Dark Rouge transports her opponent to a distinct dimension filled with green, blue, and pink orbs resembling biological cells.

Physically, Dark Rouge closely resembles Cure Rouge but adopts a darker aesthetic. Her outfit features a black base paired with dark red shorts and light red gem accents. A red and purple butterfly emblem centered with a ruby gem sits prominently on her chest. Her auburn hair features sharper bangs and forelocks curving toward her face, while the rest flares outward. Pointed ears mark her as one of the Dark Pretty Cure 5.

Her narrative concludes during the battle within the Mirror Kingdom. After provoking Cure Rouge by ridiculing her reliance on others, Cure Rouge counters by affirming the value of friendship and labeling Dark Rouge's solitary mindset as foolish. Enraged, Dark Rouge escalates her assault but is ultimately overwhelmed and destroyed by Cure Rouge's Rouge Burning attack. Unlike Dark Dream, she is not spared and reverts to her original crystal form.