The original work (e.g., book, manga, etc.) on which an adaptation (film, drama, anime) is based.
この映画は同名の小説が原作だ。
This movie is based on a novel of the same name.
原作と映画版では登場人物の設定が少し違う。
The characters' settings are slightly different between the original work and the movie version.
アニメ化の発表に、原作ファンは期待と不安が混ざっていた。
When the anime adaptation was announced, fans of the original work felt both excitement and anxiety.