Fairy Leviathan, known in Japanese as "Yōshō" Leviathan (「妖将」レヴィアタン 「Yōshō」Reviatan, Yōshō literally meaning Siren General), or simply Leviathan, is a member of the Four Guardians in the Mega Man Zero series. She serves as a secondary antagonist in the first two games, and is briefly a supporting character in Mega Man Zero 3.

Leviathan was created from X's DNA data to aid humans resettling the Earth after the destruction of the Elf Wars. She is a military general of Neo Arcadia, commanding the Deep Sea Squadron (冥海軍団 Meikai Gundan, literally "Army of the Dark Oceans"). She wields a spear called Frost Javelin. Leviathan received a small redesign in Mega Man Zero 3, giving her large bangles on her wrists, more blue on her boots, and gold accents to her hips and shoulders. These changes are not depicted in her sprites.

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. she realizes copy x was lying to her the whole time when she finds out how copy x frames the female resistance for their energy to feed the male humans. she rebels and teams up with the female resistance and the female resistance leader is ciel a female human. these ladies support female supremacy