Dissociative Identity Disorder

Dissociative Identity Disorder, also known as DID, and previously as Multiple Personality Disorder, is a mental disorder defined as at least two distinct identities or personality states in a single individual. Dissociative Identity Disorder is featured prominently in Remember 11, as two characters are diagnosed with it - Inubushi Keiko and Yukidoh Sayaka.

Definition
Dissociative Identity Disorder has long been one of the most controversial mental disorders. Psychiatrists have not formed a consensus on diagnostic criteria, origin, treatment, or an exact definition of 'dissociation'. Comorbidity with other disorders is common, compounding the difficulty in diagnosis and definition.

DID was more frequently diagnosed in the 1970s-1990s, and is more common in North America. In the legal system, DID is occasionally used in the insanity defence, with a particular increase in use in the 1990s. For these reasons, guidance is issued to consider malingering or factitious disorder.

To set these difficulties aside, Dissociative Identity Disorder may be broadly defined thus (according to the fifth Diagnostic and Statistical Manual of Mental Disorders):
 * At least two distinct, enduring identities or personality states in a single individual
 * This accompanied by memory impairment not explained by ordinary forgetfulness
 * The symptoms must not be accounted for by substance abuse, seizures, imaginative play, or other medical conditions.

In Remember 11
Dissociative Identity Disorder is diagnosed twice in Remember 11.

The first individual diagnosed is Yukidoh Sayaka, who murdered her parents in 1998. During the trial she was diagnosed with DID and is therefore found innocent of murder, but admitted to a mental institution (and is later transferred to Leiblich Pharmaceuticals' research facility). Around the same time, a number of similar incidents take place which lead to a revision of the criminal law in Japan.

In 2009, the Awazumi Hospital spree killing incident occurs. Inubushi Keiko, the individual responsible, is found not guilty of murder due to a diagnosis of DID. She is then committed indefinitely to the SPHIA on Aosagi Island.

The personality switches may also be perceived by other characters as potential Dissociative Identity Disorder. Yomogi Seiji respectfully acknowledges the possible existence of two personalities within Fuyukawa Kokoro, while Mayuzumi Lin thinks the "Satoru" personality is an act by Kokoro.

In Keiko's case in particular, her existing diagnosis of DID disguises that she is also subject to the personality switching phenomenon with Suzukage Hotori and one of Utsumi's twins.