Antonyms for the phrase "as a sequel" include "as a preface," "as a prologue," "in advance," "beforehand," and "introductory." These antonyms emphasize the idea of beginning or introducing something, rather than continuing or following it. While "as a sequel" implies a connection to a previous event or occurrence, its opposite antonyms suggest an independent start or an opening that precedes any further action. By using these antonyms, a writer can convey a sense of departure from what has happened before, rather than building upon it, and offer a fresh perspective or new direction for the reader to explore.