Momoka Sagara is the ultimate antagonist of Valkyrie Drive: Mermaid. A former partner of Mirei Shikishima, she arrives on Mermaid Island as a Soldier with the code name A3, also referred to as Françoise. She gradually seizes control of the island and acquires a substantial source of power. Momoka stands 148 centimeters tall and weighs 45 kilograms. Her most distinctive features are her light blue hair, which is tied into a bow with two long strands that reach nearly to the ground, and a cat-shaped hair clip. She has turquoise eyes. Her personality is wild, fearless, and sociopathic. She is highly manipulative and sadistic, easily deceiving others to serve her plans. For instance, she manipulates Charlotte Scherzen into helping expose Akira Hiragi's true gender and is perceptive enough to see through Akira's disguise immediately. When fighting, her behavior becomes maniacal and she shows little restraint. Momoka is classified as an Extar, a carrier of the A-Virus that allows her to transform into a weapon. However, later in the series, she demonstrates the ability to use other Extars as if she were a Liberator, such as D5 and E9. It is unclear whether this is due to experiments performed on her after being separated from Mirei, a hybrid transformation, or a unique application of her powers. Her motivations stem from her past as Mirei's partner and her desire for power, making her a cunning and dangerous adversary. Her key relationship is with Mirei, whom she once fought alongside before becoming an enemy. Momoka's development shows her transition from an undercover operative to an open antagonist who consolidates control over the island. Her abilities notably blur the line between Extar and Liberator, making her a uniquely versatile threat.