Style - the character design is good, the animation and action are amazing. 3 out of 3.
Character - There is obviously no character development because the short timespan of a movie does not allow for changes in character. But there is at the very least a semblance of a backstory and clear motivation behind the characters. Nanashi is a wandering ronin who regrets what he did in the past (killing people), and apparently likes kids. Rarou just wants to fight someone for a challenge. So at this most basic level, it works out. 2 out of 4.
Story - A bit weird. A group of about 10 Ming dynasty warriors arrive in Japan looking for a kid that they have to sacrifice on top of a tower that they just built in order to...I don't even. Okay. So a bunch of assassins are looking for a kid that they have to capture. And Nanashi just happens to like this kid. Moral of the story is don't try to kill a kid who's protected by a badass. 1 out of 3.
Overall 6 out of 10 for having undeveloped characters and a weird story.