Leviathan

In the Infinite Dendrogram anime, Leviathan is a supporting character who appears primarily in the later episodes (around the arcs involving duels and superior battles in Gideon).

She is the Embryo (specifically a Type: Maiden Guardian Embryo) belonging to the powerful player known as Behemoth (the "Beast King"). In a twist, Leviathan is the humanoid partner/master figure who carries Behemoth (who appears as a small porcupine-like creature), rather than the other way around.

In her appearance in the anime, Leviathan is depicted as a beautiful young woman in her early twenties with blue hair and blue eyes. She wears typical adventurer-style gear and often has a hat. She has a calm, somewhat affectionate demeanor toward her partner Behemoth, and she's involved in intense confrontations showcasing high-level combat capabilities.

Her role ties into themes of powerful Embryos and top-tier players, particularly in interactions with characters like Shu Starling.