First you'll need to access the steam console. Open up your Run command and enter: steam://open/console

After that, go to steamdb.info and search for Shirone: the Dragon Girl.

On the table at the top, note the AppID: 1805200 After that, click on Depots on the left sidebar. Copy the ID next to DragonGirl Content on the table. (1805201)

Click on said ID and then click on Manifests on the left. You'll have to cross-reference the updates from the games news feed to the version you want, but for simplicity we'll use the Base Version from the very bottom manifest. Copy that and note it down. (5385956804435956836)

After that, go to your steam console. In the bar, put in:

download_depot 1805200 1805201 5385956804435956836

It'll take a few minutes to download. You should eventually get a download complete notification on the console.

After all of this, navigate to your steam folder. (Drive/Program Files (x86)/Steam/steamapps/content) then click through the two folders until you get to the Shirone content. Copy the five files over the main game install folder. (Same path except common instead of content) then paste the files over the Shirone files.

Lastly, make sure automatic updates are changed for the game. Right click on it in Steam, click Properties, then Updates, then on Automatic Updates change it to: 'Only update this game when I launch it'

After that, you should be all good. The initial boot might take a moment though. After that, check the version on the top right. This guide will link you to the 1.0.0 Initial Release version.