Cocytus serves as Floor Guardian of Nazarick's fifth level, created by Warrior Takemikazuchi for martial defense. He appears as a towering fusion of mantis and ant, roughly 2.5 meters tall, adorned with icicle-like spikes and pale blue bone armor that emits diamond dust. A chilling aura surrounds him, and he carries multiple weapons including a halberd and katana. Unwaveringly loyal to Ainz Ooal Gown, he prioritizes Nazarick's honor above personal pride and embodies a warrior ethos, respecting opponents who demonstrate fighting spirit. Following a military setback against lizardmen, he evolved from blind obedience to offering strategic counsel, assuming increased independence and responsibility governing their village. He occasionally expresses envy toward fellow Guardians and desires Ainz to produce an heir, envisioning himself as their mentor. Despite general stoicism, he displays minor tender interests like arts and crafts. Academically diligent and disciplined, he leads the gym committee with strict expectations. As head of the gym committee alongside Darkness and Imperial 203rd Aerial Mage Battalion members, he enforces rigorous physical training, demanding exemplary effort during events like field days and beach trips. He views Kazuma Sato negatively for refusing competitive victory in Ainz's presence, declaring defeat impermissible. Conversely, he initially dismissed Subaru as unworthy but later acknowledged his warrior spirit after observing his moral integrity during physical examinations. During interdimensional incidents, he participates in combat against hostile entities. When a wormhole transported classmates to a world overrun by golems, he allied with Megumin, Emilia, Tanya von Degurechaff, Matheus Johann Weiss, Vooren Grantz, and Raphtalia, coordinating tactics against swarms of small golems while separated from other classmates. His background includes collecting weapons and preserved corpses of defeated warriors as trophies, honoring their resolve regardless of strength. He possesses comprehensive knowledge of divine weapons wielded by the 41 Supreme Beings, having witnessed their application only during Ainz's battle against Shalltear Bloodfallen.