Leviathan, is a member of the Four Guardians in the Mega Man Zero series. Like her siblings, Leviathan's armor is based on that of her biological origin, X, with thematic alterations. Her armor is colored blue, symbolizing her alignment with water and ice. Her helmet frames her face in such a manner as to resemble hair, with the sides forming the 'fringe' and a seashell motif forming the 'bangs'. The back is mounted with a long dorsal fin-like jet, which she uses to propel herself through bodies of water. She wields a harpoon-like Frost Javelin, the size of which she can alter, and she uses it to create ice and launch torpedoes. To highlight her femininity, Leviathan's torso armor resembles a female swimsuit, her gauntlets are long like opera gloves, and her boots have high heels. In her Armed Phenomenon form, Leviathan's armor expands to become a submarine in the shape of a gigantic manta ray, becoming much more fitting of the name 'Leviathan'. Fairy Leviathan is a playful, sadistic, and mischievous woman. She is easily bored, but takes pleasure in retiring Resistance soldiers to pass the time. She prefers to stay underwater, stating that land is "too dusty" for her. Like the other Four Guardians, she is deeply loyal to X and follows his every command.

Leviathan becomes obsessed with Zero as she fights him. She warns him not to hold back just because she's a woman