This act of "weak evil" is arguably more terrifying than Watanabe's "cold evil." Director Tetsuya Nakashima ( Kamikaze Girls , Memories of Matsuko ) uses a visual language that deliberately clashes with the subject matter. The film is drenched in J-pop aesthetics: slow-motion cherry blossoms, candy-colored lighting, and a hauntingly angelic choir singing Radiohead’s "Last Flowers."

But homeroom teacher Yuko Moriguchi (played with terrifying serenity by Takako Matsu) knows the truth.

Why the longevity? Because the film answers a question most art is afraid to ask: What if revenge is completely justified?

She had told Watanabe earlier that she would dismantle his bomb. She lied. She knew that if he thought his invention was useless, the psychological injury would be worse than any physical pain. But in the end, she realizes that mercy is not an option. She lets the bomb go off, killing Watanabe and herself alongside him.

This discordance is the point.