I must say, I think it's one of the most difficult things I have ever had to do in my entire life. They don't give you a break! The first boss (Murai), was the hardest first boss I've ever fought in any video game.
I had to return (hopefully exchange) the game because it was defected and would never get past a certain part. Anyway, I got to what I believe is the middle of Chapter(level) 5 where you fight those two Fiends. I was able to take down one of them using my 2nd level Dragon Sword and Fire Wheel, but the second one skewered me against the wall, flung me away and I died...probably because I only had an eighth of my health when the fight began.
But anyway, so far, the bosses have become easier, the third boss was easier than both the first and second bosses. The only thing I have a LOT of trouble with is those fucking black Ninjas with exploding shuriken. JESUS CHRIST, you can really only fight them with your Nunchaku, and even then you have to pay CLOSE attention to all three of them because if they land one hit, you get hit ten times and die...it's very frustrating.
i'm prolly around the same place you are...or maybe your even ahead of me now lol. But thats cuz i havent had time to play recently and i've been switching between this game and FFX-2. Once Spring Break starts for me though i'll defintely have time to start playing again. And yea those ninjas are really hard and above all just plain annoying. I just often jump a lot when i fight htem causing them to miss their throws which actually works quite well, but the drawback is that it takes longer to kill them because you can't really do that many combos on them while still constantly jumping.