These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Adaptation Displacement: Based on a novel by Ryū Murakami, though the book wasn't translated into English until 2009, ten years after the film was released, so it's understandable that the film is more well-known in English-speaking regions.
It Gets Better: People coming into this film expecting the wall-to-wall gorefest typical of a Miike film will be initially surprised and disappointed that it starts off as a romantic comedy. Stick around, boys and girls... Uncle Takashi isn't done with you yet.
Additionally, her stepfather crosses the moral event horizon the moment he pops up!
Nausea Fuel: The only time it is okay to feed someone your own vomit is if you are a bird feeding your babies. Made about a million times worse when you realize that, according to the director, this was not a special effect. It was actually Eihi Shiina's own vomit, at her insistence.
The Woobie: Subverted and possibly deconstructed. When you still think it's a romantic comedy and she's showing Aoyama her scars and telling him about the abuse she suffered, one might be expecting a love conquers all ending where he mends her tattered soul and they live happily ever after. Then things go horribly, horribly wrong.