Toru Sanada is the type of person who helps others before himself. He attends an elementary school reunion for grade 6 class 2. Back in their elementary school days, Mikio Yumesaki attended the same grade 6 class 2 with Toru and they were close. Now, being influenced by his scholar mother, Mikio plans a cruel experiment on his former elementary school classmates. He will confine them for three days and see how long their kindness can last under life-threatening situations. With the experiment in motion, Toru appeals to his ex-classmates to get out from there, but it gets worse and worse.