No spoiler warning. I'm doing you a favor.
Sakura-kun is destined to discover the secret of immortality, but the process freezes aging before puberty--so the world is full of immortal ten-year-old girls. This is, he is told, because he's a pedophile. (I think this is meant to justify, to the viewer, the violence and horror which befalls Sakura-kun in every episode, but it falls rather short of that mark.)
To prevent this, "God" sends Dokuro-chan back in time with her magic club Excaliborg to kill Sakura-kun. Instead, Dokuro-chan merely tries to prevent him from discovering the secret of immortality.
(I put "God" in quotes because the Japanese term is highly non-specific: kami-sama refers to all sorts of supernatural entities, from the Christian God all the way down to the spirits which inhabit the little shrines you see sprinkled all over anime and Japan in real life.)
First off, the main
Second, Sakura-kun is screwed no matter what he does. If Dokuro-chan goes to the future and remains there, he's dead. If she remains in our time, he's dead--repeatedly.
The one thing that Dokuro-chan does that is interesting and different is its take on angels. It's similar to that of The Prophesy, a 1995 movie starring Christopher Walken as a rather creepy Archangel Gabriel. (I highly recommend this movie. It's really good.) This quote from the main character of the movie explains it quite nicely:
Did you ever notice how in the Bible, whenever God needed to punish someone, or make an example, or whenever God needed a killing, he sent an angel? Did you ever wonder what a creature like that must be like? A whole existence spent praising your God, but always with one wing dipped in blood. Would you ever really want to see an angel?And Dokuro-chan is just that sort of angel. (More like both wings, though.)
If it was just a hyperbolic expansion of the typical tsundere'kko schtick I wouldn't mind it so much. But Dokuro-chan is not just violent but bloodthirsty and cruel, and has absolutely no qualms about torturing people (anyone, not just Sakura-kun) to get her way. The horror is treated as a source of humor, and there is nothing funny about it.
I suppose one could say that treating the horror with humor makes it more horriffic--the counterpoint emphasizes the awfulness--but the end result doesn't even approximate entertaining, and there is no compensation anywhere in the anime for that: it's not funny, it's not cute, there's no fan service, there's no real story, and there's no reason to watch it.
Trust me on this.
