Black Rat

High school student Asuka dies by suicide by jumping from the rooftop of her school, wearing a rat mask.

Forty-nine days later, six of Asuka's classmates—Misato, Kengo, Takashi, Ryota, Ryota's girlfriend Saki, and Kanako—receive text messages reading Please come to classroom 3B at midnight tonight. I'll be waiting.

Asuka. That night, Takashi, Ryota, Saki and Kanako gather.