Adapted from Hynek's classification of Close Encounters, the Fourth Kind refers to cases in which the encounter has an effect on the human mind and body. The term can also refer to a person whose body transformed beyond recognition after coming into contact with beings or phenomena related to the other world.
The term Fourth Kind is considered an extension of Hynek's classification of close encounters he wrote in his 1972 book The UFO Experience: A Scientific Inquiry. A Close Encounter of the Fourth Kind is being referred to as a UFO event in which a human is abducted by a UFO or its occupants. Although, Hynek's associate Jacques Vallee argued that the "Fourth Kind" should refer to "cases in which the witnesses experienced a transformation of their sense of reality. Also including non-abduction cases where absurd, hallucinatory, or dreamlike events are associated with the encounters.
As Kozakura explained, she adapted a concept by Hynek who divided close encounters with flying saucers into first, second, and third kind. The first kind is simple sightings, the second kind is incursions, and the third are encounters with a living creature. As the degree of contact deepens, the more people become entranced by the other world. Some get addicted, and some never return. Sorawo's right eye and Toriko's translucent hand are examples of an encounter with the Fourth Kind.