Slow, but acceptable.
For a first flash, this isn't half bad. Even so, parts of it really IS bad. But because it is your first flash, It's not really much of a big deal. First flash. First Flash.
First of, I'd like to comment on the action itself. Despite it's smooth transitions, it was a little slow. I think in a real fight it should have been a little faster, because the fight so slow I could set a world record for paddle balling before the samurai finished his sword stroke.
The song comes next. I like how it fits the setting and all, but such a calm and slightly forboding song really shouldn't be the theme for a fight scene between the ninja, a assassin and the samurai, the bodyguard. It might have fit in the beginning and maybe the end when the Ninja disappears, but not during the fight.
I thought the wounds could have been worse, because swordfights are never usually that prolonged or harmless. Especially when the Ninja hits the same place twice during the fight really put off the realism and made it look more like a choreographed fight scene I'd see in a movie.
The dash of humor was entertaining, however. The samurai wanted to eat his breakfast (?) but the Ninja ruined it and now he is sad. That made me chuckle, which is really what humor is about.
The scene of the fight could have used more shading like you did with the bamboo forest, because it looked white and bland. I didn't like it at all, the samurai was too... well.. white, and I couldn't focus on his very well. That was a huge drawback, I found myself looking more at the backround than the fight scene. I think you should have made the samurai stick out a bit more other than the fact that he was one of the two or three things moving in the entire flash.
Overall, I have to give it a 7/10. It was entertaining to watch, but leaves a lot to be desired.