I wonder how I can win against this guy
I just ate the key and saved it.
I can't do anything but fight with this guy.
The game is still being developed. More updates will arrive in the future.
To install the Japanese Language, first you must download it. Then extract the files.
Inside the download you will find 'data' and 'js' folders. Copy and Paste these folders into the English version, and say Yes to "replace these files".
(the 'data' and 'js' folders are inside the 'www' folder in the English version)
There is NO new content in the Japanese version. But maybe you will find the game more enjoyable in a language you understand better.