The unren should be in "Main game" directory, NOT the "game" directory.
Ah ha why it cd then into the \game directory because it should in the game director not into the main director you should read that:
REM Start by guessing we began in the game\ directory <---- that lines are from unren.bat and as you can see it says game directory and not main game
for %%d in ("%~dp0.") do set maindir=%%~dpd
set "pythondir=%maindir%lib\"
set "pythonlibdir=%maindir%lib\"
set "renpydir=%maindir%renpy\"
set "gamedir=%maindir%game\" <---as you can read ther it set's the maindir%game as gamedir wich is SummertimeSaga-0-20-15-pc\game in my case
set "maindir=%maindir%" <---sets the main dir what is in my case SummertimeSaga-0-20-15-pc
set ingamedir=true