1. Go to Steam, and right click on Wagamama High Spec. Click Properties. Then click Local Files. And then click 'Browse Local Files' You should get a window that looks like this:
2. Go to the DLC downloaded, called 'steamextradlc.rar'. Open this in 7zip:
3. Open this up, and extract it. Then run 'WagamamaHighSpec_Steam_R18DLC.exe' (For an example - you may need to add that folder to the extraction.):
4. When you run the DLC, you should see:
5. Run the installer. Please make sure that you have ran the game at least once, and that Steam is running.
6. Once done, run the game!