Calamity of a Zombie Girl is one of those enjoyably bad anime that only come once in a blue moon. It harkens back to an era of grindhouse B-movies, with its bizarre plot, bad characters, exploitationist themes like lesbian undertones, copious amounts of gore and random kung-fu, and in spite of all that it manages to be entertaining as hell.
A group of dumb teenagers steal a "life stone" from two (lesbian?) kung fu zombies, and all hell breaks loose as they try to get it back from them. Unfortunately, the anime suffers from that typical B-movie problem of having really boring characters standing around in a room either dumping exposition or yelling at each other, but the highlights are high enough to make the obnoxious stuff you have to sit through worth it. Occasionally, the ONA tries to get you to care about its main character (the main zombie girl), but it comes off as so hackneyed and lazy that it feels like they just threw her backstory in to make her seem less shallow. The other characters don't fair too well either, with one-note, stereotypical horror movie archetypes like "The nerd" and "The cheating girl", etc.
The animation ranges from poor to adequate. The action scenes are framed and animated in a satisfying way, while the more low-key scenes are minimalistic and shot in such a way that highlights how boring they are. My biggest gripe with the look of the show is the cookie-cutter, bland art style, which is unfortunate because it slightly detracts from the over-the-top scenes of violence that are peppered throughout the ONA's 70 minute runtime.
There are scenes of violence in this that are so sudden, so over-the-top, and so bizarre that I couldn't help but laugh uncontrollably whenever they happened, especially towards the end, however, I'm aware it's not for everyone. Heads are smashed, guts are shown, impalement and decapitation is present, and it's overall something I would not recommend to the squeamish. I think this was supposed to be a horror anime, and if that's the case they did a terrible job at making it scary, because all attempts at shock and terror came off as hilarious.
This is, by far, one of the most unintentionally entertaining anime I've seen in a while. There's a lot of dumb filler you have to sit through, but the highlights are so high that it's still worth one watch. Highly recommended for a bad movie night.