Who Killed Tokuyama Daigoro?

Keyaki Academy private school, the homeroom of Year-3 class-C. As the students arrive the find the remains of their homeroom teacher, Tokuyama Daigorou, and the group descends into chaos. "He might still be alive", "Can anyone do CPR?" The students find a knife on his back and confirm his death. This will look bad, we have to hide it. Shit, there's no time. "He might fit in there," one girl says, pointing to an area inside the classroom. "He might not be found there!" "Will he fit" "Maybe if you cut off his hands and legs..?" The bitter, callous female students of this class. A strange school life begins as the students work hard to hide the presence of their teacher's corpse in their classroom. Other teachers from the Academy, their homeroom teacher's wife, his mistress, police, and reporters... One-by-one they visit the classroom and the students face the risk of being discovered. Is it possible to continue to hide it?! And who was it who killed him?!