Trek to Yomi

This is for killing Kagerou Shogun at the end of Chapter 3, he's a pretty simple boss but the catch is if you die that's it, it carries on with the story and you missed your chance this playthrough. There is a way around this which I'll go through at the bottom of this solution, but first the fight itself.

So as I say it's a simple fight, you basically want to get used to parrying his attacks which are usually slow, over-head attacks if you use this combo, so the combo is Parry, Heavy, Heavy, Parry, Heavy, Heavy and repeat until you're low on stamina, once you're low, Parry switch with the boss (Parry and Move Forward) which will make some space for your stamina to regenerate, let the boss come to you then Parry Heavy, Heavy. And repeat until you beat him. I use this strategy in the video below if you'd rather watch it in action.

Trek to Yomi - Kagerou Shogun No Damage Taken (Kensei Difficulty) - Early End Achievement

Note: While this is technically an ending to the game you'll still be able to continue with chapter 4 after the credits roll. Also achieving this ending does not pop the Kensei Playthrough achievement (and I assume Ronin too).

The Parry Switch move can be found early in Chapter 3 where you hit the horse that kicks the cart down the road to clear a door, the horse then runs to the bottom left of the screen, go there and you'll find Parry Switch in a small area on top of some crates. If you miss it here you will find it later on in Chapter 3 as a reward for killing the first spear enemy the game introduces, although if you get it from him you miss out on another skill (Heavy Thrust).

As for the workaround to only getting one attempt per playthrough, you'll need to use the cloud saves. So after using the shrine before the fight, quit to menu and close the game, this creates a cloud save. Now load up the game and give the boss a try, if you die press , on Trek to Yomi, Manage game and add-ons, Saved data, click your Gamertag then delete from console. (Do not delete everywhere as you'll lose your save!) The next time you load up the game it will sync to your cloud save which in this case is right before the boss and allow you to try again. You can do this as much as you want until you beat him. I don't like posting this method but it's a bit annoying having to run through 3 chapters if you die, especially if doing it on Kensei like I did lol.

Do a Manual save before this boss fight, because you if you die/get enough damage the game carries on into a cutscene and there's no chapter select or reload option.
Here is 100% complete walkthrough guide for every achievement and collectibles in Trek To Yomi: