That's an extremely japanese movie. The visual style, decors, characters and their behaviour, everything is highly colourful, flashy and extravagant. There's also the cool concept of the restaurant for assassins. But it doesn't really take, it's missing a real story to glue the pieces together.

The whole beginning, before Kanako ends up at the restaurant, doesn't really serve as a good intro, is unrelated to the rest, it could be almost entirely cut. Only serves to say that she likes cooking and ends up kinda prisonner. So because she likes cooking, they make her a waitress. Makes total sense.
Obviously that's a very new, strange and dangerous environment for her, mistakes are made. Though obviously, you're waiting for the acceptance scene where seeing that she tries hard the boss will take a liking to her and make her life a little less miserable. So it kinda happens. Except it's after her fucking up so badly (people are hurt and killed level), several times in a row in a very short interval where every single incident could have been avoided had she just don what she was told to do. So the acceptance parts comes a little out of nowhere.

There's a thinly related story about the mafia big boss having been killed (mostly in the second half of the movie), but that's about it scenario wise. All the rest of the scenes (mostly encounters with diverse assassins) are just juxtaposed without any glue to make something coherent. And even there, the fact that one of the four bosses gets killed just before they are supposed to all meet is barely mentioned.

Lots of action scenes in the end, but they're exactly like the rest of the movie: it's just a succession of extravagant actions shown in slow motion, but there is absolutely nothing to tie them together. You're seeing characters do flashy stuff (shooting, jumping, avoiding bullets or explosions...) but almost always one sided, meaning you don't see who they're shooting at or fighting with. There is absolutely no global choregraphy of the fight or what's happening in it. It's almost as if the participants are not even interacting together. It's weird, boring and very long. I mean that must be the first time ever that looking at an action scene I was so drawn out of the movie and could not think nothing but how badly designed and cut it was.

Good idea, nice character and decor design, but almost all the rest fails, some part at really amateurish level.