Memetic Mutation: This GIF◊ of Shizuku writing while listening to music has become somewhat popular among lo-fi fans, thanks to several people using it (or edited versions) as a background image in lo-fi compilation videos. It helps that a lot of fans think it encapsulates what the genre feels like.
Adding various characters into the background of the scene where Shizuku is scolded by her parents at the dinner table is a popular edit to make.
Narm: Seiji's declaration of "Shizuku, I love you!" in the English dub.
Narm Charm: Despite the aforementioned Narm, it's still a very sweet scene.
Nightmare Fuel: The glowing lapis lazuli from Shizuku's story suddenly turning into a dead baby bird.
The Scrappy: A minor case but Shiho is rather unlikable because she's so bossy and demanding towards Shizuku, far moreso than their parents.
Signature Scene: The above-mentioned image of Shizuku sitting at her desk writing in her notebook while listening to her headphones has become iconic of the film.
Wangst: Yuuko's over-the-top reaction to Sugimura encouraging her to date his friend. Skipping school just because she cried the day before might seem a bit over-the-top to some.
Similarly, the way that Shizuku, Yuuko and Sugimura all treat the Love Triangle with far, far more gravitas than it actually deserves.