Okai, so, 16 high school students have been choosen by a prestigious school for their talent, so they are called 'Super High School Level' (ike the SHL Author is a high school aged book writer that had dozens of books published.) But, suddenly, they awaken in the school, completely trapped inside, with no escape.
Suddenly, a bear called Monokuma comes out, and says the only way to escape is to kill someone and get away with it. So, as soon as someone kills someone, 3 people must find the body, and then after some time an investigation with start.
If they get away with it, then they get to walk free, and the rest of the students get executed, but if they get caught, only they get executed, and the rest of the students live their lives in the school.
But, the executions are really gruesome, and have to do with their talents. I can give you a link to one of the executions, if you want to see them.