A popular series will inevitably get a Spin-Off (or Prequel or Sequel Series) containing Transplants from the original series. However, there may come a point when a character from the original moves to the spinoff at some point after it premiered.
There can be a few reasons for this. Maybe the original series ended while the spinoff is still around, freeing the person to join the spinoff. Maybe the spinoff isn't doing well, so it needs an additional character from the original to give it a boost in the ratings. Maybe the character didn't exist at the time the spinoff was created. Or maybe there is an in-universe reason that the character doesn't appear until later in the run.
This is for characters who join a spinoff as a regular. For characters who make periodic appearances only, it's a Required Spinoff Crossover. See also Sidequel.
Examples:
- While UQ Holder! was always touted as a sequel to Negima! Magister Negi Magi, early on the two series shared little in common other than Evangeline returning as a more prominent character. Seeing as the series was set roughly 80 years later, most cast members from Negima were presumed dead, including its lead character Negi Springfield. Cue the Lifemaker returning as the main antagonist about halfway into the series, possessing Negi Springfield and bringing along Jack Rakan, Albiero Imma, Nodoka Miyazaki, and Yue Ayase as companions. Debate amongst fans about whether this was a ploy to boost low ratings or was always the plan from the beginning is common.
- Rictor had been a member of the New Mutants, but left the team shortly before the New Mutants title was relaunched as X-Force. He ends up joining X-Force over a year into its title's run.
- After Bill Willingham took over Justice Society of America, he transferred villains Kid Karnevil and Blue Moon, both of whom he'd created for Shadowpact, to the JSA's rogues gallery.
- Crankshaft: "Mopey" Pete Reynolds, from Crankshaft's parent strip Funky Winkerbean. Pete basically never appeared in Crankshaft before FW ended, note but he had multiple appearances the year after it ended, including a major storyline about him buying and re-opening Montoni's Pizza (and also proposing to his girlfriend).
- After Buffy the Vampire Slayer ended, Spike became a regular on Angel during its fifth season.
- Wesley also became a regular on Angel halfway through the first season, replacing series-original character Doyle.
- Gus Fring from Breaking Bad joined the prequel Better Call Saul during the latter's third season.
- CSI: Cyber: D.B. Russell moved from the (recently ended) CSI to this series (and the other side of the country) in its second (and last) season.
- Following the cancellation of The Golden Girls sequel Golden Palace, Sophia moved to the spinoff series Empty Nest during Season 6.
- Law & Order:
- Alum Mike Logan was added to the cast of Law & Order: Criminal Intent in season 5 in order to boost ratings and allow for several non-Goren episodes after health problems forced Vincent D'Onofrio to take time off.
- Following the end of Law & Order, ADA Connie Rubirosa was transplanted over to Law & Order: LA.
- The Flash (2014): Wally West, who had been Put on a Bus, moves to Legends of Tomorrow during Season 3.
- Screech from Saved by the Bell joined the cast of the spinoff Saved by the Bell: The College Years, but after its cancellation, he joined the cast of the other spinoff Saved by the Bell: The New Class in Season 2.
- Sam Carter only moved to Stargate Atlantis after Stargate SG-1 ended, in Atlantis' fourth season.
- Worf joined the cast of Star Trek: Deep Space Nine in Season 4 in order to boost ratings.
- The Walking Dead: Morgan leaves at the end of Season 8 to find himself after the emotional trauma of the war with the Saviors, and ends up bumping into the cast of Fear the Walking Dead during their fourth season.
- Milo Murphy's Law, though not technically a spinoff, is set in the same universe and same city as Phineas and Ferb. In season 2 of Milo Murphy's Law, Heinz Doofenshmirtz from Phineas and Ferb joins the cast as a regular who now lives with Milo Murphy and is trying to become a good guy.
