Psyren is the future Japan, in the year 2018, as mentioned by Dholaki. It changes depending on the actions in the past.
The meteor Orouborous, which was supposed to miss Earth, ended up hitting the planet and releasing a substance that blocked out the sun, ruined the electronics, and left the land a wasteland that is devoid of life barring the Tavoo and "W.I.S.E", although more and more human survivors and settlements can be found with every change made to the timeline.
The atmosphere of Psyren has the ability to remove the psychic limiter on a person allowing them to use Psychic powers as well. This may or may not apply to original inhabitants of Psyren as in Psyren, only natural born psychics and drifters were able to use Psi. Either the others can have evolved to be immune to the atmosphere or never learned how to use PSI.
Psyren acts as the grounds for the game arranged by Nemesis Q, who uses pay phones as starting and exit points for the Drifters. The purpose of this game is to unravel the mystery of how the world ended up in this condition. Once the mystery is solved, the game ceases and Drifters are no longer pulled from the past to the future.
Danger Zone Edit
A Danger Zone is an area where Taboo or the W.I.S.E are found, identified by pressing the memo button of the telephone at the starting point. The telephone screen will display a circular field of dots that usually surround a Psyren Tower, representing the Danger Zone. Usually the Danger Zones are not around the starting points or the gates, but they could, as shown in Tatsuo and the Worm Arc, where everywhere is the Danger Zone.