"A divided mind is an unfocused mind. A divided mind fractures walls and weakens stone. Many divided minds may destroy a city"
― Dak'kon (Planescape: Torment)
"Utsuro. Yoshida Shouyo. I’m both of those and neither at the same time. One that has lived within this body for so long, I’ve forgotten my very name. No, maybe I never had a name to begin with. I was only showered with endless insults and hostility. And the only name I remember is… Devil."
― Utsuro (Gintama)
"If you struggle, I thrive. That's how we work."
― The Void to Robert Reynolds/Sentry (Marvel Comics)
The power to contain multiple sentient personalities within their mind. Not to be confused with Gestalt Mind.
The user is subjected to these personalities, which can be evoked at variable times. Some personas may be passive or aggressive, some may have different powers.
The separate identity inhabiting the user's hosting body is attributed as a specific symbiote. In most cases this identity can exist for an extensive period of time in which the user may have no prior knowledge of the identity's existence.
It is apparent that while these personas all look out for the original, a factor may present to have intents of over-writing and taking over as the original identity.
Clear Mind may restore the original mentality, curing the mental disorder.
Other personalities may take over the entire body permanently.
Might be hard to control.
User may not remember the other personality has taken over.
Personas may battle for control of the body. However, if the user possesses Tactile Empathy to Telepathy, they should be capable of switching their personalities freely, thus binding them into regulation. In a similar scenario, if the user has Indomitable Will, he/she can overcome the alternate personas from controlling the user.
Personas may take over when there's a certain event or if the user is under extreme stress or emotion.
If the user is unconscious or asleep, the personas may show up to claim their body.
Telepathy may be able to tell from there are other personalities, but might be difficult if the personalities have the same voices and characteristics as the original.
Mind Control may also counter this since all the personalities share the same body.
Fission Inducement/Aspect Expulsion can get bring the personality into existence but may come with a price if the personalities should get rid of the original they inhabited.
As the result of the merger of numerous Hollows, Gillians (Bleach) are mostly mindless as the numerous personalities inside of them constantly fight for control.
After nearly becoming a Hollow himself, Ichigo Kurosaki (Bleach) nonetheless developed an "inner Hollow" alter ego.
Yue's (Cardcaptor Sakura) false form, Yukito Tsukishiro, has his own identity and personality.
Aoi Fukasaku (Coppelion) awakening her other personality, Izanami.
Launch (Dragon Ball) constantly shifts between a kind-hearted, naive persona and a short-tempered, trigger-happy one whenever she sneezes.
After assimilating another being, Majin Buu (Dragon Ball series) can manifest their memories and personality to essentially cede control over his body to them temporarily.
Kaede (Elfen Lied) possesses two distinct personalities: the murderous and sadistic "Lucy" and the childish and innocent "Nyu."
Utsuro (Gintama) developed countless multiple personalities to overcome the endless pain of immortality, one such is Yoshida Shoyo, though he ultimately killed the rest of them and resurfaced.
Suikotsu (InuYasha) has two personalities: a kind, philanthropist doctor and a sadistic, murderous mercenary.
The gentle Vinegar Doppio and fearsome mob boss Diavolo (JoJo's Bizarre Adventure Part V/5: Golden Wind/Vento Aureo) share a body as two personalities, Diavolo acting as a guide and mentor for Doppio and Doppio acting as a cover and protection of Diavolo's identity as Passione's mob boss.
Jin Bubaigawara/Twice (My Hero Academia) suffered a dual personality after he got cut.
Sakura Haruno's (Naruto) hidden thoughts are frequently expressed by her "Inner Sakura," who is at times shown to be a second personality.
Cavendish (One Piece) possesses a dual personality, Hakuba, who is ruthless in slashing down everyone in range whenever Cavendish falls asleep.
Moka Akashiya (Rosario + Vampire) has two different personalities; her original haughty one (Inner Moka), and an artificial one created from her mother's rosary (Outer Moka).
Sailor Saturn (Sailor Moon) possesses both the souls of herself and Mistress Nine.
Aoi Kuchiba (The Qwaser of Stigmata) was cursed with her twin brother, Yū's personality when he accidentally killed him.
Harumi Chono (Paranoia Agent) has two very different personalities.
Maria (Paranoia Agent) a prostitute, Harumi's alternate ego.
Kenshin Himura (Rurouni Kenshin) struggles with his assassin alter ego Battousai the Manslayer...
...who's dominance of Kenshin's mind is signified by Kenshin's eyes turning golden.
Sensui (YuYu Hakusho) has seven personalities, one counting his own and six others.
Alice (Bakugan) with her mask can take on her altered ego, Masquerade. Not only her looks and voice (and probably gender) has changed but Masquerade's personality is the complete opposite of Alice's.
Touko Fukawa (Dangan Ronpa) mostly unwillingly switches to her murderous alternate personality, Genocider Syo, and back through fainting or sneezing.
Zofis implanted a strong darkness inside Koko’s (Zatch Bell!) heart in order to make an ideal partner. By infusing the darkness with Koko’s hidden pain and jealousy, Zofis created a separate personality who enjoyed hurting others as much as he did. Zofis used this evil Koko as a partner while keeping her true, kindhearted side locked away.
Kolulu (Zatch Bell!) has a separate personality inside her spellbook. Whenever Kolulu’s bookkeeper Lori reads the spell Zeruku Kolulu’s sadistic side is released.
Diana (Marchen Awakens Romance) acquired a sinister and heartless personality because of the Chess Pieces’ king’s mind control. Unknown to everyone, even herself, Diana’s true kindhearted self is still locked away.
Under the effects of the Joker infection and Scarecrow's fear toxin, Batman (Batman: Arkham Knight) developed a split personality based on the Joker.
Quincy Sharp (Batman: Arkham) has a murderous split personality that believes itself to be the spirit of Amadeus Arkham.
Brigade (Marvel Nemesis: Rise of the Imperfects) constantly struggles with the minds of the one hundred Iraq War soldiers whose corpses make up his body.
Raiden (Metal Gear) has been overtaken by his "Jack the Ripper" persona.
Revolver Ocelot (Metal Gear) used hypnosis, psychotherapy, drugs, and nanomachines to transplant the deceased Liquid Snake's thoughts, memories, and mannerisms onto himself, creating a split personality dubbed Liquid Ocelot.
Elisa and Ursula (Metal Gear Solid: Portable Ops) are split personalities who believe themselves to be the other's twin sister.
The Prince of Persia (Prince of Persia: The Two Thrones) developed a second personality, the Dark Prince, when he was corrupted by the Sands of Time.
Legion (Mass Effect) possesses the combined minds of over 1000 geth programs.
Alfred Ashford (Resident Evil) developed a split personality based on his twin sister Alexia after going insane from loneliness.
Evil Ryu (Street Fighter), Ryu's persona when he has been overtaken by the Satsui no Hado.
When to pass strict age limits, Penelope (Sly Cooper: Thieves in Time) invented a disguise, giving herself under the alias, Black Baron, a pilot who wins the ACES Flying Competition each year.
The Black Knight (Sly Cooper: Thieves in Time) is another persona Penelope took under while working for Cyrille Le Paradox.
Hyde (Valkyrie Crusade) has a split personality.
Noire (Fire Emblem Awakening) developed a more brash and violent split personality as a result of being used as a test subject for her mother Tharja's curses.