One of Umineko no Naku Koro Ni's Seven Stakes of Purgatory, and representative of the deadly sin of envy. Second oldest (even if she doesn't often act it), with the only wholly unnatural hair color (green) of the Stake Sisters. Since all the sisters have red irises, perhaps the closest she can get to being the green-eyed monster is to be the green-haired monster.
The human she is based on is Lenon.
Named after Leviathan, a Biblical demon/sea monster.