Season 0 of Kansen premiered on November 1, 2013.

Season 1 of Kansen premiered on October 30, 2009.

Yasuyuki is a high school student in love with his classmate, Yuu. He decides to join her film club to be near her. The teacher, Shindou Risa, and club members plan an overnight training camp on school grounds during summer vacation; Yasuyuki jumps on the opportunity. However, they are unaware that a virus is within the school, making those infected experience intense lust…

Season 2 of Kansen premiered on February 26, 2010.

Kansen 2 takes place during the initial outbreak of the Unknown virus epidemic, but the protagonists here have a much harder lot because they are stuck in the middle of a contaminated city immediately after its destruction by a mysterious cataclysm. Stalked by hordes of infected maniacs, Hiroshi Ookura and his friends seek safety inside a mostly intact shopping mall, but madness and death are everywhere...

Season 3 of Kansen premiered on September 24, 2010.

Four years have passed since the initial outbreak of the Unknown virus epidemic, and the terrifying plague which depopulated the Tohoku region of Japan has been reduced to a mere memory, thanks to drastic quarantine measures coupled with an effective vaccine.

But the Unknown virus is not dead yet and soon, very soon, an inescapable doom will fall upon Wataru Ayase and his family and friends, trapping them inside the "Hell on Earth" madhouse which originally was their home city, Tokyo...

Season 4 of Kansen premiered on October 26, 2012.

Oogami Island is normally a peaceful isle with lush green scenery, but is now a place of depraved wanton lust. The contagion Unknown - Level 4 has become epidemic. 3 girls, Hyuuga Natsu, Ochi Akari, and Hanazawa Airi find themselves trapped in a sports facility where they are assaulted by the infected.