Yakuza games use 2 different models for major characters, one for gameplay, with lower quality textures, and one for cutscenes, with higher quality textures. This mod basically merges cutscenes textures with gameplay models. Similar to FluffyQuack's Valkyria Chronicles mod

In general face textures and tattoos are improved for the major characters. Kiryu and Majima got more improvements. They're kind of very subtle, mostly visible in the close up in some substories.
Textures themselves are 4 times bigger. They're taken straight from the game, so there should be no issues with inconsistent art style of textures, since they were made by the original game devs.

Before:

After:

Just in case you might want to backup "Yakuza 0\media\data\chara\w64\adv" folder

You can download the mod from this Nexus Mods link[www.nexusmods.com] or from PC Gaming Wiki.[community.pcgamingwiki.com]

Extract the file and copy the media folder over to game's root folder

There's also a guide for Yakuza Kiwami, Yakuza 5 and Yakuza 6
https://sp.zhabite.com/sharedfiles/filedetails/?id=1660775310 https://sp.zhabite.com/sharedfiles/filedetails/?id=2377709072 https://sp.zhabite.com/sharedfiles/filedetails/?id=2439765454

Yakuza 3 and Yakuza 4 already have applied high resolution textures, so there's no need for mod, however for Yakuza 3 you can download High res mod by O1Gamer[www.nexusmods.com] that further replaces the textures that for some reason were left from gameplay models and my high res Majima's jacket mod[www.nexusmods.com], which quite drastically improves the jacket textures.