An otherwise boring high school boy, Kasuga, is tempted by the left-behind gym clothes of his crush. Startled by a noise as he picks them up, he runs off, only to find that he has inadvertantly stolen them. Terrified, he hides them at home. Shortly thereafter, he finds out that Nakamura, a rebellious member of his class, saw him steal them. Using his secret as leverage, she blackmails him into a "contract," though what it is or what she wants remains ambiguous until the end of the series.
Story: Basically involves Nakamura continuing to be a busybody, Kasuga trying to normally date the girl whose gym clothes he stole, and other dramatic events. The story is heavy with themes of guilt, conformity/rebellion, the awkwardness of being a teenager, depression, and the face-saving behaviors Japanese people engage in, including sweeping your own emotions under the rug and maintaining your facade. It's almost a Japanese Catcher in the Rye, and what I really liked about it was its realism.
Animation & Sound: I thought the voice acting was top notch. This is real Japanese language, not the cartoony voices you'll find in most other shows.
The animation technique used is rotoscoping. People seem to love it or hate it. The backgrounds and character designs were extremely realistic, which, again, I think fit the themes of the show.
Characters: It's hard to cheer for any of them, and the story really brings out their flaws, rather than their good qualities. Personally, I think that's just the way a good story should go: the characters keep falling prey to their own weaknesses, insecurities, and habitual bad decisions. I also loved that Nakamura was so hard to figure out; I never knew what she was going to do next or what was really running through her head.
Overall: Really meaty themes, highly unusual and realistic art, excellent voice acting, and fascinatingly human characters.
Aku no Hana is not a happy show, and is probably not for everyone. If you liked Catcher in the Rye or A Dead Poet's Society, I'd highly recommend Aku no Hana to you. If you don't know much about Japanese culture, don't like the rotoscoping technique, or find depressed teenagers overly melodramatic, this might not be a good watch for you.