The curious case of Serial Experiments Lain.
In a way I am happy to have stumbled upon on it 17(!) years late. On the one hand, it is eerily prescient and interested in fascinating questions of subjectivity in an increasingly virtual world, things we grapple with to this day. On the other, as with most technology-heavy narratives, there are aspects of the story that have become dated or seem silly. That said, it's own internal logic is sound, and any datedness can almost be treated as if the story is taking place in an alternative timeline.
Lain's enormous influence on early 2000s pop science fiction cannot be overstated.