Cocytus is the Type Maiden with Advance Embryo of Hugo Lesseps.
Cocytus takes the form of a young girl entirely dressed in white, with a white dress and a white ushanka hat. She also has blue eyes. When transformed into her Advance form, she takes the form of an ice armour that covers whatever device Hugo is riding.
Cocytus has a spunky personality, being unafraid to criticise her own master or even the leader of their clan.
Due to the basis of her ability, Cocytus can get a general feel for how many people from their own race someone has killed.
Crest Conceal: A skill that allows a Maiden to get a Master's crest so as to disguise themselves as such. Any Maiden will learn this skill as a result of fighting by themselves.
La Porte de l'Enfer(地獄門): This skill applies the Freezing debuff to all targets within a certain range every 13 seconds, with X% percent of their body being affected with an X% chance of success, where X is the number of beings from the same race that the target has killed. The Freezing debuff applied from this skill cannot be negated by normal Freezing debuff resistance. The length of time the target is Frozen depends on the value of X. The Freezing debuff is activated by absorbing a target's heat via the air, so anyone in an airtight environment is immune to the skill.
- Purgatory Flash(煉獄閃): Cocytus takes all the heat absorbed by La Porte D'Enfer and transforms it to a blade of heat energy for direct combat.
La Porte de l'Enfer Duexieme (第二地獄門): This skill applies the Freezing debuff to X% of a target's body, where X is the damage Hugo or his vehicle has taken from a target multiplied by the number of beings from the same race the target has killed divided by the targets HP. The Freezing debuff applied from this skill cannot be negated by normal Freezing debuff resistance. Damage received also takes into account damage negated by items or skills. Cocytus received this ability after evolving to her fourth form and after Hugo received the MFGX-02 White Rose from Mr. Franklin, so the ability is predicated on being used with this Magingear.The Freezing debuff is activated by absorbing a target's heat via the air, so anyone in an airtight environment is immune to the skill. Cocytus and Hugo note that the ability is influenced by their encounters with Ray Starling and Nemesis.