They are classified into two groups: the transmitters and the receivers. The transmitters send information through the field and the receivers receive information through the field.
The Morphogenetic Field Theory, first discovered by British biochemist Rupert Sheldrake, explains how two humans can send messages through an invisible field, similar to telepathy.
Although why and how someone becomes an esper isn't entirely explored, there are implications in the series that espers possess higher consciousness compared to the other humans. One could interpret espers as those being chosen by "god" or a higher power.
Accessing the morphogenetic fields and esper powers are affected by two things. Those things are epiphany and danger, and while not required, they boost one's ability to access the field. By how much is unknown, but assumed a significant amount. Epiphany is explained as the feeling of when one is working on a difficult problem and the answer just sort of "pops" in their head. The second factor, danger, is required to be life or death.
First Nonary Game and Second Nonary Game
Gentarou Hongou wanted to be able to control the field to cure his prosopagnosia, so he had children that went to one of his hospitals tested to see if they could access it. It was then that he used his assets to set up everything he needed for the First Nonary Game. One night in 2018, nine pairs of siblings, 18 children in total, who were able to access the field, were kidnapped by Hongou and other Cradle Pharmaceutical officials.
The siblings were to be split up, 9 of them being on the Gigantic and the other 9 inside Building Q. There was a mistake on the arrangements however, and Akane and Aoi Kurashiki ended up on board the Gigantic together, while another unknown pair of siblings ended up together in Building Q. The game soon begins. The transmitters in Building Q were instructed to send help on getting through the escape rooms to the receivers on the Gigantic to have them escape. These kids included Clover Field and Ennea Kashiwabara. This was possible because the layout of both areas were nearly identical. Akane and Aoi are joined by Light and Nona, along with 5 other unknown children aboard the Gigantic. With help from the transmitters, their group finally made it to Door 9 in the incinerator.
The five unknown kids frantically left the unfortunate others behind, going through the 9 door. The kids left behind were Nona, Light, Aoi, and Akane. The incinerator suddenly activates, and the four trapped kids seemingly have no way out. Suddenly, a detective named Seven comes out through a vent up on the wall of the room. He drags the kids up to safety with a "towel rope" and eventually, they find their way to the staircase. They quickly dash up the stairs, in fear of Hongou finding them, but as they were almost to the exit, Aoi notices that Akane was not following them. Aoi insists that the group go back for her, and Seven and Light tag along, with Nona continuing towards the exit. The three get there as soon as Hongou is about to throw her into the incinerator. He succeeds in doing so and locks the doors behind him. Then, Hongou escapes through a back door in the incinerator, and activates the burning process.
A computer suddenly comes up out of the floor, with a sudoku puzzle on its screen. Hongou informs her that he had left the bracelets that will help her stop the incineration process, but it will not activate unless she solves the puzzle. Ignoring his information, she tries to authenticate, but it doesn't work. With no options left, she reaches Junpei through the morphogenetic field, who is in the same situation in 2027. Hearing her cries for help, Junpei quickly gives her the solution, which allows her to survive in the past. Before she escapes, she leaves 5 numbers on the computer: 2, 4, 5, 7, 8. These are the numbers that the players inside the room with Junpei possess, and he quickly figures that they should authenticate at the 9 door, even though their digital root is 8. Because the door was actually a "q" instead of "9", it worked and Junpei and his companions escape safely.
The remaining players hop into a SUV that the Kurashikis have left behind and eventually see a hitchhiker on the side of the road. This turns out to be Alice, who was a member of the SOIS and was going to investigate what was happening inside Building Q. She questioned the others and released them all except for Hongou.
Some time later, Alice gathers up the players who had participated in the First or Second Nonary Games and asks them to join the SOIS for their esper abilities, in order to fight Free the Soul. Clover and Light decide to join.
In December 2028, while looking for the Myrmidon headquarters in Los Angeles, Alice and Clover were abducted for the Nonary Game: Ambidex Edition by Akane. They were frozen in treatment pods until 2074, when the game actually begins. On Phi's route, it was discovered that Clover and Tenmyouji were participants of the game for their esper abilities, which heightens Sigma's and Phi's esper powers and their ability to jump through timelines. Akane Kurashiki can also send her consciousness through time because of her esper powers. It is currently unknown if Clover and Junpei can do the same.