Strange Resurgence, I Awaken the Necromancer System

Travel to a parallel world a hundred years after a strange recovery. In this hundred years, only one tenth of humanity is left, and the number of ghosts has exceeded humans! In order to survive, everyone must choose a "companion ghost" from the moment they are born, and then they must continuously increase their bond with the companion ghost, so that the ghost can control the ghost. Su Ming, who traveled through time, suddenly discovered that he had awakened the Necromancer system. Not only can it summon the dead, but it can also contract with other ghosts. Moreover, with the help of the system, ghosts can be easily upgraded, which makes the ghost controllers in this world feel very incredible about this...