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The game takes up 30+MB, but the installer is 369MB.


The Humble Bundle version has a 40+MB installer.
Most likely it also contains installers for dependencies, like DirectX or .NET framework. ;)
Another possibility is that the huge size of the download file is caused by the Japanese version. In this case, I would be curious to find out WHY the Japanese version is so much bigger, double-byte characters alone don't explain it - more or different content?