Wow, it is so sad. I couldn't stop crying. It is undoubtedly a shock at first, being not at all used to seeing sex displayed so obviously on the screen. But, well I mean we are all mostly no strangers to the sexual act. So after you get over the initial embarrassment, the film is very deeply touching.
The actors are extremely convincing, even taking into account the poker-faced, non-expression that the japanese seem to practise. You see them spiralling down, further and further into the danger of addiction, of it never being enough, always needing more, a heftier kick. A gigantic itch that gets worse the more you scratch. It is so terribly sad because you know they will destroy each other with their love and desire and there's nothing you, or they can do to stop it.