Most characters, like most people, live one life beginning to end. While Time Travel, Alternate Dimensions and the occasional Body Swap can complicate things, they are still more or less one person, starring in one life, for one lifetime.
Except when they're not. Because every now and then, a story stars a character who lives multiple lives, not serially, but alternating between them one day at a time. It's not that they leave one and travel to the other; they physically exist continually in each world, but their consciousness alternates between them.
These separate lives may take place spread out across time or in Alternate Universes. The character will often have to gather information between their lives in order to advance the plot. Their unique circumstance makes it possible to talk to people that died in one universe before they could deliver important news or lets the main character save someone in one universe by figuring out who killed them in the other.
Sister Trope to Non-Linear Character.
Not to be confused with Alternate Self, where the two lives are lived by two similar but separate people who happen to look alike and have the same name. Compare with Reincarnation. Contrast with Living a Double Life and Split Personality where the "multiple lives" are discrete aspects of a single life kept apart by design or mental disorder.
For the video game trope involving extra lives that allow the player character to survive otherwise fatal encounters, see 1-Up.
- In the Sherlock fic "The World on His Wrist", John Watson begins waking up to the lives-in-progress of 4 very different John Watsons after he is wounded in combat with the RAMC in Afghanistan. At first, it's all he can do to juggle four confusing lives without being caught out. But once he gets the hang of it, he uses the various lives for escapism, to gather information, and to save lives as a doctor and a soldier and something like a non-costumed superhero... and then he meets Sherlock Holmes.
- In Sleepless every time Harry fell asleep he ended up in an alternate universe where he had to defend their version of the Malfoys against an attempt to legally execute them.
- In Twilight Zone: The Movie a racist man is shuttled back and forth in time to live lives as a black, Jewish, and Asian person. He was supposed to learn a moral, but due to the death of the actor while filming an action scene he gets sent off to the gas chamber as a Jew during World War II.
- In Dark Corners a woman alternates between the lives of an affluent young woman about to get married and a mortician's assistant living in a squalid apartment in a dangerous neighbourhood, never sure which is real and which is a dream.
- In the short story "The Other Wife" by Jack Finney, a man discovers a way to travel between alternate realities. In each one he is married to a different wife, and when he finds himself getting bored with one he returns to the other.
- The central premise of Ted Dekker's The Circle Series is that Thomas Hunter receives a head injury and wakes up in another world. The action is then split across "our world" and that other world: every time Hunter falls asleep in one, he wakes up in the other.
- A science-fiction novel Dayworld had as its premise that the entire world was divided into seven populations which took turns being active one day of the week each, while the other six are in stasis. The protagonist is a man who illegally maintains separate lives in each of the seven days.
- Awake: Main character Detective Britten suddenly begins switching between two universes every time he falls asleep after a car crash kills his wife in one universe and his son in the other. While his therapists in each universe try to convince him that the other universe is just a trauma-induced dream, he isn't so sure. Across the two lives, he begins to notice suspicious coincidences which he investigates seeking an explanation for what's happening to him which leads him to the heart of a dangerous conspiracy where he needs the time and information from both lives just to stay one step ahead of his enemies.
- Doctor Who has had several examples of this in its run:
- In the classic episode "City of Death", it's revealed that the Monster of the Week, the Scaroth, is living multiple lives throughout Earth's history simultaneously, and using his shared knowledge of these lives to further his plans.
- In the modern episode "Amy's Choice", the Doctor, Rory and Amy keep going back and forth between two sets of lives — one where they're all on the TARDIS and one where Amy & Rory are living on Earth & she's pregnant — and have to decide which is the "right" timeline.
- In the Series Finale of Star Trek: The Next Generation, Captain Picard is living in three alternate timelines, one in his past, one in his present, and one in his future, at the same time, and has to use information gathered in certain timelines to aid others.
- The Twilight Zone Classic episode "A World of Difference". Arthur Curtis finds himself switching between two worlds - one where he's a normal businessman, and another where he's an alcoholic actor named Gerry Raigan who's playing the role of businessman Arthur Curtis in a movie.
- In the Stargate SG-1 episode "The Changeling" Teal'c alternates between his life at Stargate Command and another life where he and the other SG-1 members are firefighters. Both seem equally real. In truth, neither is real. He's hallucinating due to sharing his symbiote with Bra'tac after they were both shot during an ambush by Anubis' forces.
- The Outer Limits (1995): In "Tempests", Commander John Virgil, the first officer of the spaceship Tempest, is infected with the venom of a giant alien spider which causes him to hallucinate. His perspective begins to switch between two mutually exclusive realities: one in which he is hailed as a hero for delivering the serum that eliminated the virus Ellycia C that was devastating his home colony and one in which he must repair the severely damaged Tempest so that it can bring the serum to the colony. He must decide which is real and which is the illusion. It turns out that neither is real and that the unconscious Virgil is trapped aboard the Tempest being fed on by one of the spiders, as are the rest of the crew.
- Sigma and Phi in Virtue's Last Reward can send their consciousness across multiple realities, where certain major events have happened differently (their physical representation still lives through and experiences these events, but their mind can go just about anywhere in the course of the AB Game). After jumping to a new reality, they can occasionally retain some knowledge of what they've learned without knowing how they know it, to push the plot of that reality forward. By the end of the game, they're fully aware of this, and use it to their advantage multiple times.
- Homestuck: One of the features of SBURB is that players have an additional body, their dream self, who begins the game in a tower on Prospit or Derse. Once the player awakens their dream self (usually via a personal epiphany or extreme shock) their consciousness will shift between both bodies: when you sleep in one, you immediately wake up in the other. There are a few variations on this setup such as Dirk Strider, who's fully awake in both bodies, simultaneously.