Thousands of years later, the events of Nier occur, and doom humanity to extinction. The world was now entirely populated by these engineered doppelgangers, each with new personalities and souls, and it's here (around the year 3361) that the events of Nier occurred.

What killed all the humans in NieR?

After a brief battle between the two, the Giant collapses and the Dragon perishes after being shot down by human fighter jets. This bizarre incident marks the beginning of the end of humanity. By December of that same year, a mysterious infection that is eventually dubbed "White Chlorination Syndrome," or WCS, appears.

Are the people in NieR Replicant human?

For the Japanese version of the game, see NieR RepliCant. The Replicants are soulless artificial bodies created as a part of the Project Gestalt.