Gemini, Japanese title Sôseiji 双生児, which could just as well be translated "Twins," although that isn't very creepy, which this movie is supposed to be. It was directed by Tsukamoto Shin'ya 塚本晋也 and released in 1999. Based on an Edogawa Ranpo short story which has been translated (as "Twins"); good story, although most of what's in the film is Tsukamoto's fantasia on Ranpo's themes.
A bit hard to follow at first, but pretty soon you're entranced. Imagine David Cronenberg remaking something from Suzuki Seijun's Taishô trilogy: that's this film. An elegant, classy setting for some truly sick jewels.
And it's the setting that I found myself drawn to, more than the jewels. The crime, the violence, the horror felt very Ranpo, which is to say sort of Poeish, and therefore were more or less what I expected. But I loved the film's vision of late-Meiji/early-Taishô Japan.
Weird hairstyles. No eyebrows. Lines clean, clothes neat, behavior unbelievably poised. Until you get to the slums, which are Dickens on acid. The period details, in other words, are recognizable, but defamiliarized. This is past-as-foreign-country stuff, exoticizing early 20th-century Japan, putting domestic audiences in almost the same position as their foreign counterparts vis-a-vis the country's past. Sort of the opposite of nostalgia. Very interesting.
Mokkun, by the way, is great in it. Even without eyebrows.