The demo for Valkyria Chronicles 3 is already out on the Playstation Store in Japan. Sure, you can go and make a Japanese account and deal with signing into the Playstation Network to verify the demo or you can just click the link below to download.
[Click here to download] [Size: 152mb]
It should take you to a page that looks like this, but should pop up a download for you. Enjoy!
[Source: 4Gamer]
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Downloading now. Thanks for the post.