Yakuza Kiwami

So far it's easier than 0s climax battles

Agree with the above advice dragon in proving grounds 9 is the way to go. Proving grounds 1, proving grounds 3, proving grounds 8 and mad dog 3 are pretty brutal otherwise not too bad so far. Just starting the ultimate challenges.

Fuck mad dog battle 3...

Yakuza 0 Climax Battles were a smooth sailing for me. I did all of them in a few hours. However Kiwami battles really took a toll on me. I think it is much much harder. I spent 10+ hours on them and completing some of them was pure luck. What is weird though that I didn't have problem with the ones most people mentioned. Since Yakuza 0 is relatively fresh for me I think enemies got way more aggressive while Kiryu got much weaker. Enemies were mostly punching bags and high heat levels allowed you to beat through their defenses and attacks in 0. Here however everything stuns you, the enemies ruin you mid combo and some bosses are ridiculously fast while the devs remove basic tools from you.
Here are some (maybe) useful advice for the mode:
If you aren't hard pressed for Tiger Drops it is a very viable tactic to kite around enemies in Brawler (purple) then run up to someone who is away from the group/boss and quickly land a short combo on him. A few of these attacks activate the lowest heat bar moves very fast. Afterwards You can land the heat move in any style and go back to Brawler right away. This helps a ton with safely chipping away the lackeys of a boss who won't give up running after you and ruining your day. Related to this if you have your Dragon abilities unlocked - and the timer isn't a problem - use your heat to Sumo Slap safely someone in the group. You heal a bit that way! You can heal a lot if you don't use a finisher heat move on bosses but beat them up and slap them over and over. Outside a few cases, like Zombie Majima in Mad Dog 3 I don't suggest using heat move finishers at all. Most of the time you can keep the healing at bay by punching and your heat bar will be maxed out for the next fight. There are plenty of cases where it is crucial to land a Brawler "tornado" move right away (with full heat grab someone and Y in the middle of a group) to clean up some people asap. Most of the moves provide very unreliable results in this game but this move has a high chance of KOing even small bosses in one hit.
For specific encounters:
Proving Grounds 8: You have to kill the guy in the light suit before the others because if he will be the last he will only do his jump kicks and Tiger Drop doesn't connect with that. At least I couldn't do it. The bad news is he usually hangs in the back so good luck.
Melee Battle 5: if you don't have enough heat when the staff guy appears to instantly KO him with a big table move then you are dead. He will stunlock you and won't let you get up ever. This took me ridiculously long because something always blocked the prompt.
Mad Dog 3: So I got this for the second try. What I noticed is that the bicycle (on the left) heat moves deal a lot of damage and you can bait Majima by pressing X once to hit the air from a reasonable distance and evade behind him right away. If you have a lot of health and he doesn't then deliberately letting him to hit you and counter hitting him is surprisingly effective to make him die before you.

I think melee battle 10 is harder than anything proving grounds throws at you

that comment about ultimate battles being the easiest i cant agree at all right now id put them at on on par or the hardest in the game right now they are the last i need to beat and idk if i can beat them

Melee Battle 10 is absurd, my tips gathered from others online are the following:: Pray that Kashiwagi doesn’t obliterate your health early on and when you get to Sera: leave the two guys with projectiles alive to farm heat. Train Sera around the courtyard and when you have heat: Heat Action one of the lampposts on him. Be warned that he’s just like in Y0 where he can stunlock conbo upwards of 40% of your health. If you dont have enough heat to finish him off you can get him to aggro from a safe distance with the wood fence on the rightside of the courtyard between the garden and the walkway

Hardest for me were Melee 10 and Proving Ground 8. All were easier than that Y0’s Ultimate 5 imho though

In Proving Grounds 9, I struggled to build enough heat to consistently do the beast heat action like in the video, but finally finished it using a tip I found elsewhere.
Using a heat action in Dragon style will give you back some health, so if you do a few of those throughout the match, you don't have to worry so much about a stray hit now and then, and the challenge becomes pretty trivial.

Mad Dog 3 is a joke as long as you make regular use of Brawler’s Tiger Drop variant; guarding while (the last) Majima attacks works just fine too.

Also, anyone that says that these Climax Battles are easier or are better than 0’s are lying. Melee 10 is complete bullshit no matter what way you slice it, and the Ultimate Battles, while not hard, are sure as fuck miserable.

If you can beat Yakuza 0's climax battles, you can beat these and will have an easier time as well.

Obscure Tip:
I read a post somewhere on TA where an unfortunate soul had this achievement glitch on them. They had to wipe their save, beat the campaign again, and redo all the climax battles. I felt bad when I read this, but I can at least try to prevent it from happening again.

If you're afraid of this rare bug (it usually triggers when you play from instant on), there is a simple precaution you can take. The game saves your climax battle progress, but only when you back out of the climax menu and return to the main menu. And more importantly, this achievement should immediately unlock after finishing the final climax battle.

Therefore, if you're unlucky enough that the achievement glitches on you, go straight to the Xbox dashboard and quit the app from there. This will prevent the game from saving your progress and locking you out of the achievement. Load the game back up and try the final battle again.