Sometimes an anime has such subtle foreshadowing that fans watch the series over and over, hunting for clues of what unfolds later in the series. Even if an anime's foreshadowing is ham-fisted and plainly in the face of the audience, it's still effective because it adds tension and audiences can't help but ponder how foreshadowed events will unfold. Other times, obvious foreshadowing is a hint that trope will be subverted with a vengeance.
Source：https://www.cbr.com/anime-foreshadowing/
