We think based on similar images, that this image is from 120 Yen, a digital novel that was included on a fandisk from Japanese PC game developer Neko Neko Soft.

Installation: After unzipping your download, place the package in your mod folder, found at C:/...Documents\Electronic Arts\The Sims 4\Mods

Note: You can only have one CAS background in your mod folder at a time.

In game, go to Options | Other | Enable Custom Content and Mods and check that the "enable custom content and mods" and/or "script mods allowed" is ticked. Reboot game and find the new background in your CAS.