The major thing that you need to know about Blood is that it's only about 45 minutes long. Thus it is not an overly complex, layered, moody drama. The characters are incredibly basic and, to be honest, a little flat. That's OK though, because with its moody visual style and solid pacing Blood succeeds at being a tight, entertaining piece of animation.
Blood opens with a stylish, comic book-y kill on a moving subway. The killer is a gal named Saya, and, while her origin is never explicitly explained in the movie, it is implied that she is the last vampire. After the subway fight Saya meets up with her employers, two mysterious men in suits, and it is here that we are given the set-up for the next 30-some minutes. It seems that Saya's speciality is demon hunting, and that her skills are in demand at a school located in Tokyo's Yokota Air Base.
This plot device works for a number of reason. First of all, as the Yokota Air Base is an American military base, it gives the filmmakers an excuse to record about half of the film's dialogue in English. Yes, while portions of Blood are in Japanese and subtitled, a good majority of the movie is in English. I did a quick bit of Internet research on this and apparently this was done to speed up the process of selling the film to American audiences. While I was initially distracted by Blood's bilingual nature, I grew used to it pretty quickly and overall having the two languages worked more than I would have thought that it would.
Blood's setting also works to create a number of interesting visuals in which Saya's look, that of a young Japanese school girl, is contrasted by her stoic personality and violent actions. Similarly I was impressed by a sequence in which two demons disguised as students shed their innocent looking disguises and transform into monsters. What impressed me about this was how subtle the transformations were. When Saya initially slays one of the demons there is a brief moment in which the viewer is unsure of whether she has struck down a young student or a monstrous creature. It isn't until we see a gnarled, inhuman hand amongst the blood splatter that we fully realise the true identity of the student.
I would like to point out that all of this stuff could have looked really bad if it wasn't for the stark, gritty style in which Blood is animated. Staying away from the cliche cotton candy colored haircuts and outrageous fashions of some anime, Blood's style is realistic and bleak. There is a distinctive color scheme to Blood's world, and that color scheme consists blacks, browns, greys, and other muted hues. The movie also makes unexpectedly good use of CG animation to add an impressive depth to the movie. There is a school dance scene early on, in particular, that I felt I could walk right into if I had wanted to.
Blood isn't going to blow your mind with intricate storytelling, but it is 45 minutes worth of eye candy with a solid enough plot to keep you engaged the whole time. I can recommend it heartily for what it is. Enjoy!