Breaking the 4th wall is nothing new and has been done a million ways since the days of Shakespeare, but Fleabag's use of the 4th wall is the first time I've seen it powerfully used as a dramatic tool that becomes part of her character's psyche and the story itself.

It doesn't seem too significant at first, other than a really funny way of delivering punchlines, but in season 2 something weird happens and one of the other characters, the priest, begins to notice her asides, eventually getting freaked out by them, and suddenly Fleabag's whole comfort wall starts to crumble. I didn't think too much of this, except that it was a really interesting development, but I just stumbled on a very cool video where someone breaks down the breaking down of the broken 4th wall (wha?) and it turns out it really makes sense to the story and how things eventually turn out.

Why there can never be a 3rd Season of Fleabag