My 2nd Solution so far. Sry if my English is not to good for you, but i will try my best. I will try to give various tips on every day (especially bosses and sm hard fights). If you still have a hard time in a specific battle in the Story, then write a comment and i will update if i can. Okay lets get started.
Here is Ninja Gaiden 3: Razors Edge Ultimate Ninja. This achievement requiers to beat the Story Mode on the hardest difficoulty. To get this Difficoulty, you must beat Ninja Master first (to Unlock Ninja Master simply beat the game once on Normal or Hard).
1. Before you start this,i recomnend to train a lot with your weapons. Best bet is the Scythe to beat this game, even this weapon is cheap. Use circle Y (360Y). Most enemys r easy to kill with this. However against harder enemys like the chimera, you should not spamm the 360Y. Do 1 360Y then dash and simply do 360Y. I call it the Attack, Dodge, Attack Tactic.^^
2. Try to use the Ultimate Technique or Steel of Bones as much as often as you can. The reason is you have a Chance to heal yourself a little bit.
3. If you r hard wounded, then you should run back to find a skull. If you leave the challenge you r healed and you have also a checkpoint.
4. Save your Ninpo and your health bar. Use it when your in big trouble. I recomnend to use the health bar by the boss fights.
5. On some Levels you can mostly ignore the fights. For example on day 5 you must only fight 15% of all Matches.
6. Another good tip is to watching Videos via Youtube or so.
7. Almost forgot: Use on Day 1 the scarab Glitch, to get much Karma as soon as possible. Without that it would be a pain in the ass.
8. You only need 45 Scarabs, cuz 50 unlock only costumes. So you dnt need to collect all Scarabs.
The first Level isnt so hard. For the beginning spamm the UT and try to dodge the enemys. Against the Dogs you use UT or throw the kunais. Right after your 1st savepoints you will fight against a lot of enemys + alchemists. It can be troublesome but there is a good trick to beat every enemy without getting a hit. Jumpf over the sandback and use UT. This works against the Alchemist as well, since they cant hit, no matter what.
After your savepoint you have 1 more fight. After that there r rocket guys who r killed from an helicopter. in this place you should look at a scarab. Try to use the Glitch because you will meet the first boss soon.
Boss 1 Spidertank:
This fight is easy. If you have true Inferno, simply use at the Start. That destroy his armor legs and that 1 rocket launcher guy. If not, kill the rocket launcher first, and then the armor legs with 360Y Scythe (beware of new rocket launcher guys).
Boss 2 Masked Man (Theodore):
Go near to him and use twice 360Y and then dodge, and repeat. He isnt that hard, if you know how to do it. The same Tactic goes on Day 7 and Day 8.
How i hated this Level. Normally it isnt that hard, but the most Problem are the helicopters and the boss. Against the helicopters use the bow while you jump or you can try this: dodge -> bow -> dodge -> bow etc. It can sometimes really annoying since they can kill you very easily.
Boss 3 Big Helicopter:
Well, lets have some fun :D You fight this Boss in multiple Phases. Shoot him with the bow and if your Timing and luck is right, you will hit his rocket while he is shooting at you. If you hit it, you will damage him. Thats all what you have to do. The most Problem i have was the last phases. There r spawning flying rocket enemys. It can be troublesome, but dodge them and if they landing you use the flying swallow (A+X) + Y.
This Level isnt hard. At the start simply spamm X,X,X against the weak enemys. After this match find the scarab and use that glitch again. Otherwise you will have Problems. There isnt much any tips but i would recomnend (after you have enough Karma) to do the Izuna Drop. Against the big Fiends (i call them Mini-Marbus) spamm the 360Y, but dodge as well.
Boss 4 3xBlack Alchemist:
They can be annoying, but try to Focus on 1 Alchemist and spamm 360Y. You can also use your Ninpo as well, but use it when all 3 Alchemist are near by you.
Most of the Times you will use the 360Y Scythe, but you will meet the helicopters again. First dodge against the rocket attack from them and then spamm with your Bow Tactic (Attack, Dodge, Attack Tactic). When you reach the tower, there is a lot of enemys like chimera and those "monkeys". Use UT and Steel of Bones and you should be fine. The best and save spot to do this fight is near where the scarab is.
Boss 5 Donisaur:
This boss is easy, but he can give you a 1-2 Hit Kill. Dodge on the ground (never jump, thats important) and when this beast fall down, use 360Y (any weapon but Scythe is best). This 2 fights goes in 2 Phases and the tactic are the same.
This Level can be troublesome, cuz there are some fights you will may have to dodge a lot. The most troublesome spot is the very very small room at the end. The reason is there are many soldiers, a couple rocket launcher, 3 Spiderfiends and a couple white alchemists. The room is really small. If you fight against the spiderfiends, then shoot their armor down, after they landing on the ground use a ninpo. Its makes a lot of damage. If they wounded and still alive, go near and dodge and use Y while he is attacking you. That will kill the enemy quickly.
Boss 6 Lovelace:
1 of the easiest Boss in my opinion. With 360Y combine with Attack, Dodge, Attack Tactic, you should be fine. This boss fight should be ended in 5 Minutes. Also dnt try to jump around, but you can use the flying swallow (A+X) + Y, when you are in the corner. Use Ninpo when your health is low.
Dnt waste any Times, simply dodge and ignore every fight you can. If you do it, you will finish this level in around 15 Minutes. In the second part, Momiji will accompany you and this makes a lot easier.
Boss 7 Obaba:
Another easy battle. You have to kill various enemys before you can attack this boss arms core (you will see them when they glowing). Normally this boss fight is quickly over, but the last part has a lot of enemys + tentacles. If you have Ninpo, use it against the enemys. This boss has a lot of quickevents, so prepare to use the A and X Buttons.
The difficoulty of this level depends on your skills cuz there are various battles that can be hard. But if play every Levels before, then you should know your tactics against your enemys. Mini-Marbus and those pink big Fiends -> 360Y Spamm, Spiderfiends -> If possible use Ninpo, otherwise 1x 360Y and Dodge. The annoying "Clawfiends" (i hate, hate, hate those enemys), simply try to go to a corner and spamm 360Y until they are dead. Dnt try the Izuna against them cuz they dodge your attacks very often.
Boss 8 Clon Ryu and Epigonos (Dark Ryu):
I hope you are prepared for an glitchy boss. Boths are normally the same. The Tactic is (what i tried) 2x 360Y then dodge and repeat. If Epigonos use a Ninpo or his UT simply use flying swallow (A+X) + Y or you can try (if your are really close to him) the steel of bones.
This Level is easy, BUT there are 2 fights against enemys that can be really frustrating. The first fight is the place where the black alchemist will spawn. You have to fight against rocket launcher and soldiers before you meet them. Try to save a UT for the alchemists. If the alchemists comes, dnt use it. Wait until at least 1 alchemists comes towards to you, and then use that UT. Normally it should kill at least 1 Alchemist. If not, do the same tactic as Day 2-Ayane.
The 2nd fight is are real pain in the ass. You have to fight against tons of enemys. The worst thing is, you have to fight against the white Clawfiends. They are really annoying, but jump away and use the UT, and they should be kill very easily. If Mini-Marbus spawning, then kill him first (with 360Y spamm) before you attack the other enemys. if your health is low then use Ninpo and ONLY 1 health bar.
Boss 9 3x Lovelace Clones:
If you have at least 1 health bar, then you should win this Bossfight easily. Concentrate at 1 Boss and spamm 360Y, but to be save do the Attack, Dodge, Attack Tactic since the other Bosses wouldnt not standing around the whole time.^^ This fight isnt that hard, it just like a Dodge Party. You can use a Ninpo as well, cuz it makes a lot of damage to them.
There isnt much an advice for this level, cuz you have to fight nearly every enemy. I think there isnt a hard spot, but on 1 place you will the Clawfiends, Mini-Marbus and 3 Spiderfiends. Kill Mini-Marbus first via 360Y and then the Clawfiends with 360Y or UT. Dnt waste your Ninpo. Use the Ninpo for the Spiderfiends. The rest of this Level isnt hard.
Boss 10 LOA Chairman:
This Bossfight is hard, if your Health Bar is low. This Fight goes in 3 Phases. The first Phase is his standing Dragon Form. You have to destroy the Arms. Wait until he attacking you with 1 of his Arms (1 do the Flamethrower and the other 1 will do that Lightning "Ramming on the ground" Attack) and then use 360Y until his Arms are destroyed.
The 2nd Phase is really easy. You only can use your Bow. The main Problem is (you will see it) his Laser Beam. Dnt rush to him, do the opposite and run to the other side. Dnt his Laser Beam by the right Moment.
After the 2nd Phase you will see that he fall down on the Ground. Also here you can only use your Bow. He will run towards to you really fast. Shoot at him at every Moment you have but dnt forget to dodge. You can also use a Ninpo but right after the Ninpo you must dodge. Be careful he can kill you (depends of how many health you have left) with 1-2 Hits. At the end he will use the Laser Beam again. Dnt dodge, simply wait until he comes to you. And then slide under him and use X-Button for an Quickevent.
Welcome to the final Level. Here you can ignore the most fight too. So dnt worry about to much. There are only a couple fight you have to do. Use everything you learned about this game and use UT, Ninpos etc.
Boss 11 Cliff:
This Bossfight is really easy. You only have 1 thing to do: 360Y combine with Attack, Dodge, Attack Tactic. In the middle of this Battle when Cliff flying around, there are spawning a couple of White Clawfiends. You shouldnt have any problems against them, since is only a couple of them. After that Cliff landing back and you can kill him.
Boss 12 (Final Boss) Goddess:
This Bossfight is hard, really hard, if you already have uses all of your health bar (like me). It goes in 2 Phases.
1.Phase: In my opinion the worst and hardest Bossfight i ever have i any of the Ninja Gaiden Series. The Concept is so bad that it will frustrating you. You must fill up your Ninpo while you kill the White Clawfiends. Mostly it will spawns 4 of them. The Problem is that the Boss screams out a lot (very annoying) and shooting you with projectiles. Also she use her big Arm to hammer on the building. This is a real Dodge Party. To make it easier use the Moonstaff and simply spamm the UT. 1 Time on the left side then Ut, dodge and go the right side and UT. Rinse and repeat.
2.Phase: Fortunatly the White Clawfiends are gone. However she will rarely use her Arm. If she doing that use the 360Y Scythe twice. Yes twice. I found a trick to dodge her sword after you hit her.^^ Anyway, stay on the right side the whole time, until her life bar is at zero. You have to run back to left side and waiting for the final Quickevent. Congratulations you finish the Game on the hardest difficoulty.