Here you all go, very difficult to find, and extremely expensive, and super complex application process to merge with the game files as we feared might happen. Unfortunately I can't upload it here since they discovered unbreakable DRM file protection so you'll have to pay 100 USD too:
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Good luck, make sure to watch the twenty hour youtube tutorial on how to code in Japanese first!!
P.S. Don't mean to offend, it's just... kagura's games have worked this way since the very start of their company afaik.
P.P.S. I don't recommend actually jumping right into it the day of release, their games almost always need some bugfixes. Tho hopefully since this one was in development hell for so long it came out perfect! Anyway, if you give it a week or two then play the inevitable v1.02 or v1.05 it usually makes for a better gaming experience.