1.
prologue, opening chapter, prelude
The introductory section of a book, story, or other work. Also used figuratively to describe the beginning phase of a larger event or development.
Usage
Used both literally for the opening section of a written work and figuratively for the beginning of a larger chain of events. The figurative usage often carries ominous or dramatic overtones.
Common patterns
Similar words
序文 is the author's preface or foreword, while 序章 is the opening chapter of the narrative itself.