Sequel

A sequel is a work of literature, film, theatre, television, music or video games that continues or expands an earlier work; in fiction it "portrays events set in the same fictional universe as an earlier work, usually chronologically following the events of that work," often with the same characters and settings, and a run of sequels becomes a series "in which key elements appear repeatedly." The commercial logic is old and explicit: there is "less risk involved in returning to a story with known popularity," and eighteenth-century publishing used sequels to profit from and defend literary paternity amid weak copyright. Akira Kurosawa's Sanshiro Sugata Part II (1945) was the earliest numbered sequel in cinema.

For novelists the sequel is the series decision: what changes, what repeats, and what the previous book's ending left to build on. Keeping multiple books consistent, characters, world rules and timeline, is the job of how to write a series and the story bible.