For the record, I'm way over 20, and I watch anime as a serious film genre (serious as in "it's a legitimate form", not as in "no fun"). This piece of trash is hardly worth your time. The "plot", if you could call it that, is about as thin as tissue paper. The token fan service scene is there, but it's hollow as well, and there's exactly one of them. We do get to see exploding skulls a few times, but they come across as more the artist saying "look! I can do disgusting!" They're gratuitous and don't do a thing for the movie.
Seriously, you skip this. It's worthless, even as a piece of anime history.