At the end of season 6 of Star Trek: Deep Space Nine:
Jadzia Dax is killed.
At the start of season 7:
A “new” character, Ezri Dax, the next host of the Dax symbiont, is introduced.
This results in quite a few episodes in the first half of season 7 featuring Ezri heavily (including three full “Ezri episodes” — Afterimage, Prodigal Daughter, and the god-awful Field of Fire). I assumed this was an intentional attempt to get the audience to care about the character before the big finale of the show kicks into gear.
But it does seem like a lot of effort to go through at this stage in the show. Bringing in a whole new character just for the last season seems like an odd choice. Although it was really interesting to explore the same-symbiont, different-host thing, and Nicole De Boer did a great job with the character, were there behind-the-scenes reasons for Jadzia being written out?