There are several saves in the archive:

New Game+ saves with saving leveling and items
Saves before boss battles
Saves at the beginning of each chapter
Save for achievements

Place all files here:

<Steam-folder>\userdata\<user-id>\1088710\remote\ (Steam)

%LOCALAPPDATA%\Packages\SEGAofAmericaInc.Yakuza3PC_<ALPHABETS>\SystemAppData\wgs (Microsoft Store)

<Steam-folder>/steamapps/compatdata/1088710/pfx/ (Steam Play, Linux)

Author: MITSUYOSHI