Below is the description provided by noko12312 on his original upload on ModDB (found here). I am sharing his work here with his permission.
This mod replaces the character textures during gameplay with the same (but higher resolution) textures that are used during the cinematic scenes. Texture resolution is 4x larger than the original gameplay textures. You wont notice too much of a difference unless the camera is close up on a characters face. These are from the game files themselves, so it wont break immersion. Comparison pictures link in description.
Comparison Pictures here: Imgur.com
Extract and place the data folder where your Yakuza0.exe is located (typically Steam\steamapps\common\Yakuza0\media)
Overwrite the files when prompted
Thats it. Enjoy!