Yuuko Moriguchi, a middle school teacher, resigns from her position after a tragic accident at the school results in the death of her four-year-old daughter, Manami. Having previously called off her engagement, Yuuko had found her sole purpose in life through her child. Before leaving, she delivers a final lecture to her students. During this lecture, she reveals a story that challenges their perceptions of two of their classmates, initiating a complex plan for revenge.
