In case anybody in the future can't figure out why this issue occurs, I'm here to solve your problems and tell you where you went wrong.
To get this error message, this is what you would have had to have done:
Step 1: Download Hanahira
Step 2: Extract Hanahira Zip File < - - This is where you screwed up
Step 3: Get unicode gibberish and panic
Step 4: Change region locale to Japan
Step 5: Open setup.exe, see an error message in Japanese and be confused
Step 6: Try to reinstall under different conditions
Step 7: Profit
The reason the INIファイルの読み込みに失敗しました error occurs is because it cannot locate the INI file. Why can it not locate the INI file? Your folder names are in unicode gibberish, not Japanese! This screws up the file path referenced in the setup.exe file. Changing your region locale did not fix the folder names. You solve this issue by extracting the zip folder once again, this time with your region locale set to Japan. You don't have to do this on a USB drive. Extract it anywhere you like.
This time, when you open up setup.exe, it will find the INI file and all will be well.
So, really, what you should have done was:
Step 0: Change Region Locale to Japan
Step 1: Download Hanahira
Step 2: Extact Hanahira Zip File
Step 3: Open Setup.exe and install Hanahira
Step 4: Play Hanahira and profit
You're welcome.