At some unknown point in the future, many of the people on Earth who were implanted with HPlus Implants and connected to the wireless network suddenly died. Those who were not online survived, as did those who were not implanted. Billions died across the world, and disasters and death are widespread in the aftermath.
Presumably, the Event was caused by the Tsumi App, created by LPW and spread globally through the HPlus users a few weeks prior to the Event.