Bloody Monday (stylized in all caps) is a Japanese manga series written by Ryō Ryūmon and illustrated by Kōji Megumi.

A second series, Bloody Monday Season 2: Pandora no Hako, was serialized in the same magazine from October 2009 to April 2011, with its chapters collected in eight volumes.

The Public Security Intelligence Agency's Third-I section hires Fujimaru Takagi, a skilled hacker known as "Falcon," to decipher the chip, which includes a video file depicting a viral epidemic in Russia that kills thousands, known as the Christmas Massacre.

Things become even more complicated when Fujimaru's father, a high-ranking officer inside Third-I, is wrongfully suspected of murdering his supervisor after learning more about the Christmas Massacre, later receiving the code name "Bloody Monday."

From there, Fujimaru struggles to know who he can trust as he utilises his high-level hacking abilities to try to save the country and solve the mystery of Bloody Monday and the cult behind it.