Cocytus

Cocytus (also known as Cyco in her disguised form) is a key character in the Infinite Dendrogram anime. She is the Embryo (a unique AI partner) of Hugo Lesseps, a Master from the Dryfe Imperium who pilots giant mecha-like vehicles called Magingears.

In the anime, Cocytus initially appears under the alias Cyco, presenting herself as another player/Master to hide her true nature. She is eventually revealed to be Hugo's Maiden-type Embryo (specifically a Maiden with Advance type), taking the form of a young girl dressed entirely in white, complete with a white dress and ushanka hat, giving her a striking, icy aesthetic that matches her powers.

Her abilities revolve around ice and cold-based effects. She can merge with Hugo's Magingear to dramatically enhance it, granting the mech ice armor, freezing attacks, and powerful wide-scale suppression capabilities (such as heat-absorbing/freezing debuffs that punish enemies or deal massive damage). This fusion turns Hugo into a formidable combatant, especially against groups or tough bosses.

Cocytus is loyal to Hugo, often blunt or calling him out, and her powers tie into themes of justice and punishment (stemming from Hugo's backstory). She plays a significant role in several episodes, particularly during intense battles where her true identity and merged form are showcased.