Prequel

[Gregory]

A story or film containing events which precede those of an existing work.

[Raeanne Dimick]

In literature and entertainment, a [sequel] in which the events [depicted] or described take place before the introductory story. This practice originated with [George Lucas], who started producing the Star Wars series with the fourth episode in the mid-1970s.

[Lanell]

To [ejaculate] too [quickly]

[Monty]

a film, book, or play that develops the story of an earlier film, etc. by telling you what happened before the events in the first film, etc.: