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 guide will allow you to merge cutscenes textures with gameplay models. Similar to FluffyQuack's Valkyria Chornicles mod or my Yakuza 0 mod

In general face textures, some clothes and body textures are improved for the major characters. 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.

Comparison, click on the pictures to see more:

From Nexus Mods[www.nexusmods.com] or Google Drive[drive.google.com] download the file "Packaged" file.

Extract the archive and copy and paste "data" folder into your Yakuza 6 folder.

(If you can't download the file from Google Drive due to transfer limits, right click on the folder and select "Download", which will compress the file and let you download)

This is more advanced installation that requires you to use ParTool[github.com] with "add" parameter.

From Nexus Mods[www.nexusmods.com] or Google Drive[drive.google.com] download the "DIY" file.

Example of installation:
Extract the archive and copy the "chara" folder into Yakuza 6 folder\data.
Copy the ParTool.exe into Yakuza 6 folder\data.
In Yakuza 6 folder\data create .bat file with contents "ParTool add chara.par chara chara1.par -c 0" or "ParTool add chara.par chara chara1.par -c 1", if you want compression, and launch it.
Rename "chara.par" into "chara.par.bak", and rename "chara1.par" into "chara.par"

Available on Nexus Mods[www.nexusmods.com] in both easy and manual ways.

An optional version of the mod.
Adjusts to brightness of Kiryu's suit to make it appear closer to his vanilla gameplay texture.
Install it the same way as mentioned in "Installation (manual way)"

On top of that, you can use Solidical's mod to force cutscene models for Kiryu in gameplay, which is available on Yakuza Modding Community Discord.
This way you'll get even better Kiryu model.

There's also this kind of mod for Yakuza 0, Kiwami and Yakuza 5, if you're interested
https://gtm.steamproxy.vip/sharedfiles/filedetails/?id=1465239828 https://gtm.steamproxy.vip/sharedfiles/filedetails/?id=1660775310 https://gtm.steamproxy.vip/sharedfiles/filedetails/?id=2377709072

Yakuza 3 and Yakuza 4 on PC already have high resolution textures installed out of box, but 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.