Lisa Takeba goes full horror. Comparisons with Battle Royale are easy to make, personally it reminded me more of Miike's Lesson of the Evil and As the Gods Will. A sunny day in an average Japanese classroom ends up a grim and bloody quest for survival, a perfect premise for 90 minutes of slick entertainment.
The kids find themselves at the mercy of their teacher. He has shown them a video that has hypnotized all of them, leaving them with 100 trigger actions that forces them to commit suicide when performed. The problem is that they have no clue what these actions are, and doing anything out of the ordinary may lead to their untimely death.
It's a fun premise, the performances are solid, the kills are bloody (though not every kill is quite as original) and the pacing is slick. It's a bit of an adjustment to see Takeba handle this type of material, but she does a good job. 100 Signals is a perfectly fine and enjoyable horror film, food for genre enthusiasts.