Dark Lemonade is the dark counterpart to Cure Lemonade, forged by the villain Shadow using Mirror Kingdom crystals fused with Cure Lemonade's powers. She embodies Cure Lemonade's past self, fixated solely on personal happiness while disregarding others. Physically mirroring Cure Lemonade with blonde hair and yellow eyes, her attire adopts a darker scheme: a black dress featuring neon yellow accents, including a V-shaped waist trim, paired with gold shorts. Her pigtails are thicker, styled as twin drills with curled ends.

Her personality is brutal and cold-blooded, reflecting a self-centered worldview. She scorns Cure Lemonade's belief in songs spreading happiness, instead weaponizing her vocal abilities into destructive sonic wave attacks. In combat, she employs techniques like Darkness Flash, swinging her legs to unleash yellow energy blades, and utilizes offensive sonic waves generated through singing.

Within the movie's conflict, Dark Lemonade confronts Cure Lemonade in a mirrored dimension of statues and pillars. Their battle intensifies as Cure Lemonade asserts songs should foster joy, not harm. This clash culminates in Dark Lemonade's defeat by Cure Lemonade's Lemonade Shining attack. Unlike Dark Dream, Dark Lemonade experiences no redemption; she is destroyed, reverting to her original crystal state.