Here's a save file that has cleared the game, just as a note this isn't a 100% complete file, but there's a lot of completed stuff, including creator clan and the bouncer missions, and all upgrades. I have posted a guide like this for all the other Yakuza, Like A Dragon and Judgment games. Links to all of them can be found here and on my profile. The links can be found here and on my steam page:
https://sp.zhabite.com/sharedfiles/filedetails/?id=2689025548
https://sp.zhabite.com/sharedfiles/filedetails/?id=2585769811
https://sp.zhabite.com/sharedfiles/filedetails/?id=2586740791
https://sp.zhabite.com/sharedfiles/filedetails/?id=2379715518
https://sp.zhabite.com/sharedfiles/filedetails/?id=2389968624
https://sp.zhabite.com/sharedfiles/filedetails/?id=2408950501
https://sp.zhabite.com/sharedfiles/filedetails/?id=2440359743
https://sp.zhabite.com/sharedfiles/filedetails/?id=2447367563
https://sp.zhabite.com/sharedfiles/filedetails/?id=2864943075
https://sp.zhabite.com/sharedfiles/filedetails/?id=2872921349

Saves:
https://drive.google.com/file/d/1nK4-wlp_I5v2tThG2UAgk_CNK5ZCtOF7/view?usp=sharing

Amon Save:
https://drive.google.com/file/d/1Ud6aWgY0c6BR6KNnkN5tYVWIqT2Ma3Cw/view?usp=sharing

Both:
https://www.nexusmods.com/yakuzakiwami2/mods/393

Please rate and favourite if these guides have helped you! Awards are nice too but not necessary.

Premium Adventure Hard is in slot 01, Premium Adventure Legend is in slot 02, Bouncer save is in slot 03.

Save 13 is the Amon save, you can rename it to any save and it should work. The Amon locations are: the parking spot near kanrai, behind serena, theatre square, the champion district and then finally millennium tower. Use the beam sword and muscle soda, heat attacks work through shields but however, using heat moves you have already used will not work at a certain point, use all your weapons.

After downloading the folder, unzip it using 7zip or winrar, inside is a folder called yakuza Kiwami 2 saves open the folder and copy the files, this part is different from every other Yakuza game so pay attention, you may need to make hidden folders/files appear in windows to find this folder, search google on how to do this. To find the folder go to your taskbar and type in %appdata% a folder called roaming will appear, from there go to roaming\Sega\YakuzaKiwami2\ <user-id> \ and paste your saves there. If you are confused look at the images below.
I recommend backing up your own saves, just in case. You might need to turn off steam cloud for Yakuza Kiwami 2 for this to work, to do that, right click on Yakuza Kiwami 2 in your library and go to properties and you will see a tickbox under steam cloud in general.

Enjoy, kyoudais