My screen resolution is 1920 x 1080 and I went into Onigiri's options and changed its resolution to what I thought was 1920 x 1080 and set it to fullscreen but it's so large now that I can't access any buttons at all to change my settings back and I literally can't do anything but log in, which I can do only because I can proceed to the next screen by pressing the enter key.

Also there's no taskbar icon for it so right now in order to quit the game I have to end it through task manager.

http://s20.postimg.org/xchhhzxuj/onigiri.png

If you cannot access the buttons or play the game properly due to the screen resolution being too large, please navigate and delete the temporary files in the folder located at:
C:\Users\USERNAME\AppData\Roaming\cobra

USERNAME would be replaced with the name of the account you are logged in with. If you cannot see the AppData folder, please look into how to "Enable hidden files" for Windows.

Once the folder's content been deleted, please restart your client and the screen resolution should return to its default size. Please note this method resets all other settings on your game client such as graphic and audio settings, as well as your saved username and password.

If your fullscreen is running too big, then perhaps your windows display scaling is set to medium or large?

Have you tried reducing it back to 100%?

Or try the compatibility mode and tick the box that says "disable display scaling on high DPI settings".

Thank you Ramune. It works.