Uuuuh.
How to explain, without spoiling...
EDIT:
In a nutshell.
15 kids > Hopes Peak Academy > Pass out upon entering
Upupu bear > dispair dispair > trapped inside the school > Kill and don't get found out during the class trial > punishment for murderer > sadness > plotwist > Dangan rumpus 2
Double edit:
Its basically a game of Ace attorney except a bit more execiting.
Theres' a prestgious school dubbed "Hopes Peak Academy" it accepts only the most elite students. The Ultimates. (Or Super High School Level Talented, if you like typing that)
Example: Ultimate Programmer, Ultimate Fighter, Ultimate Pop Sensation.
It is said once you graduate, you basically have a one way ticket to success and prosperity wherever you go.
You play as a boy, Makoto Naegi. An average boy with no ultimate title. Until he gets selected in the annual school lottery for average people attendants. He is then dubbed the 'Ultimate Lucky Student'
Upon entering the halls of hopes peak, he faints. He wakes up with a group of 14 other students all ultimate titles.
They are sealed in the school as there are no exits. There is a monochrome bear named 'Monokuma'. He wants to spread dispair, he informs them that if they wish to escape, they must murder one of their classmates and undergo a class trial where they must not be caught. They will then 'graduate' from the school and be free to leave. The only issue is that if they are not found out in the CT, all the other students are executed/punished. If they are caught, the murder is the only one murdered. And thus the mutal killing life continues.