Interesting horror flick. At first sight, it looks a lot like other, often game-based, Japanese high school fantasy horror films, where kids are locked in at night and strange things start happening to them. But Grand Guignol adds some unexpected slasher folklore and isn't stingy when it comes to blood and gore.
A small, secluded school only takes on troubled students. There's a study group that tackles the Grand Guignol novel, and soon enough the school is facing a similar murder case. A masked demon is haunting the students and killing them in cold blood, The problem is that almost everyone is a suspect.
It's not often you see clear slasher influences in a Japanese horror. Add to that the overt violence, LGBTQ characters, and a pretty cool killer, and you have a film that is more than just another generic horror rip-off. Fans of (Japanese) horror cinema would do well to give this one a shot. Not for the faint of heart though.