I'm a librarian who loves anime, manga, and reading a wide variety of genres.
Only a week later, they're all back in the house. To be fair, only one of them actually remembers everything that happened.
I'm guessing the "vengeance" part of the title refers to the poor kid who was bullied into killing himself prior to the start of the first book. He didn't technically get any closure, so I guess it's time to start killing his tormentors (and anyone who happens to be standing nearby) for real.