Yakuza Kiwami 2

Legend mode is unlocked once you finish the game for the first time. Once you fully upgrade your abilities in premium adventure legend mode is easy. Once you are able sell enough to the weapons dealer to unlock the photon sword GL this is the fastest and highest damage outputting weapons and buy the gun he sells since it is infinite and has a high damage output, no fast shoot in this but if you do not stance up and just shoot it is fairly fast. If you want you can play legend mode the same as your first play through. If you just want the achievement then you can skip 90% of all dialogue scenes in game. If you can not you can speed up dialogue the same way as 0 and Kiwami where you hold down and . Still keep an abundance of healing items on you because there is no health regenerating item like in Kiwami. The gun and rocket enemies do a fair amount of damage even with defensive items equipped. I used the amulets in my play-through and made it through just fine. SAVE OFTEN! Any time you feel you are about to get in a rough fight or complete a chapter save since if you game over you must load your previous save. Finally, make sure with the final fight with Ryuji to be ready for the final button prompt or you will need to load your last save. The achievement will unlock once you get to the final save screen after your stats screen for the play-through.

Note: For Osaka castle when you get to the part with the gattling gun be sure you are not using the sacred wood armor or Kiryu will block every time he is shot and leave the gun turret forcing you to manually chase the shooters down.

I want to start of by saying that if you need help with certain gameplay aspects (Osaka Castle for example), then please read firestormworld guide for this achievement too! They also have great advice about armour and some other weapons that are extremely helpful for this run.

What you want to do here is complete the Majima Saga either as each part unlocks, or just wait until you have all 3 parts unlocked and then do them all at once. During this saga, Majima is asked to donate money to Kiryu by the Kazama Family, so, if you follow this hidden items guide by CyricZ, you should be able to find items to pawn off (as Majima) and you will need to donate 3,000,000 yen to Kiryu. Once you are back as Kiryu, you will have a package at either Aoi or Serena, in that will be "Gifts from Majima" and, if you donated the 3 mil, Kiryu should get the Prize Gun as a gift. Then you want to take that to Kamiyama and sell it to him, this will have his store unlock powerful, infinite weapons. Buy any one of them, it really doesn't matter, I personally used the Illegal Poison Kodachi, but the Photon Blade W or RG is an extremely popular choice for this too, as is the DRAGON-SP (only unlocked in Premium Adventure). Naturally, make sure you are as levelled up as possible before then starting New Game+ in Legend difficulty.

Another tip, to make this go even faster for you, stock up on Muscle Soda (Green vending machines) whenever possible and whenever needed. If you use those, coupled with the infinite weapons, you are set and this playthrough shouldn't take you long at all.