It's been a while since I've played this game. The game is based on an anime called Death Note (that I have not seen) where 3 notebooks will spawn in certain parts of the map and the players who find it gets to be Kira.
You have to be secret with your notebook and pick up IDs without being seen, then choose how that player loses. You have to work with your teammates to accuse innocent players to win. If no one dies for 2 rounds, the game spills the tea on who Kira is.