After some more testing I found a way to fix the game without downloading anything and using the somewhat broken beta version of the game. Step 1 Fixes there being no fullscreen option, Step 2 fixes the blackscreen issues.

Step 1. Switch to the beta version of the game by right clicking the game in your steam library clicking Properties then going to the Beta tab finally switch to the beta version.

Step 2. Go to the local files tab click browse go into the Kokoneo folder and then delete the save folder.

And finally you should be able to play the game. If it doesn't work you cause use the old fix for the game posted below.

To make the game fullscreen add -popupwindow to the launch options

• Thanks to doing a decomplation of the game it appears fullscreen options was disabled in code and I've made a patch to make the buttons work again. (Located in the kokonoe_Data folder in the zip)
  
• Added missing game files to download to fix blackscreen (If they aren't needed don't add files from the save folder to game otherwise it will reset all settings)

Place the folders inside the game files in order to patch the game.
https://mega .nz/file/b9kyxJBQ#A8e8BcpJ2mCBlTu5vRclApQVCxQogyO_jx_0aPxHdow
(Remove space to get download link)
God what has my life come to...