Charybdis

It is not entirely certain what Charybdis is. She and Celeste Hardouin believe that Charybdis is the original personality that existed in their body. During the time period where Charybdis inhabited Celeste's body, Celeste was dominant, with Charybdis only occasionally gaining control in certain circumstances. Instances where Charybdis has taken control were typically characterized by a sharply increased drive for violence and causing pain, followed by adverse physical reactions in the body (profuse sweating, coughing, etc.) as Celeste attempted to regain control.

As it stands, Charybdis is no longer physically tied to Celeste, though she has a strong desire to regain her body from Celeste.

Charybdis named Celeste's sword, Scylla, after her mythological counterpart.