Here's a save file that has cleared the game, with this you can either start a brand new game on legendary difficulty, use the old file as a new game plus and unlock some achievements, just as a note this isn't a 100% complete file. 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

Kiryu Clan "final fight", Clear Game and Amon Fight Saves:
https://drive.google.com/file/d/1tEdLCbbO1bubn7NbOuqQwuGeXbrv6b8Y/view?usp=sharing
https://www.nexusmods.com/yakuza6/mods/122

Please rate and favourite if these guides have helped you! Awards are nice too but not necessary.
Save 1 is right before the final fight with JUSTIS, it also has all of the clan creators code characters added, you're welcome.
Save 2 is right before the final fights, you can also fight Amon if you want, just take a taxi to fight him.
Save 3 is in Premium Adventure Mode with the Amon fight active as well.
Save 4 is for reaching 200 in every stat for an achievement, just go to stats and upgrade the last one.
Save 5 is for buying all other skills for an achievement, just go to stats and the other skills tab and buy all the remaining skills.
Save 6 is for 300 in every stat for an achievement, just go to stats and upgrade the last one.
Save 7 is for reaching level 99 for a character in clan creator for the achievement, should work both with and without the DLC also on the final clan battle against Amon in Ono Michi, with 3 level 99s so makes it easier, for the level 99 just go to training and level up Majima or Ono Michio (or both.)
Save 8 is furthest progress wise, for people that want to 100%, this includes all substories completed and all clan battles, also contains 99 won clan battles for the on the winning team achievement. If the the all substories complete achievement doesn't get given to you, you might have to use save 7 to do the baseball and hostess stuff, I'd upload a save right before the final substory but I forgot, but that stuff is fairly easy so you can do it!
Save 9 is the right before the final fight on legendary, incase you wanna skip legendary (It only took 3 and a half hours this time but even so I'm nice so here you go.)

After downloading the folder, unzip it using 7zip or winrar, inside is a folder called Yakuza 6 Saves open the folder and copy the save folders, go to where steam is installed and click steam, userdata, [your steam ID], 1388590, remote and paste the folders there. I recommend backing up your own saves, just incase. You might need to turn off steam cloud for Yakuza 6 for this to work, to do that, right click on Yakuza 6 in your library and go to properties and you will see a tickbox under steam cloud in general. Enjoy, kyoudais