This paper records that the earliest origin of the Dual-Layer Universe Theory (Koku/Genki Universes, verbalized 2026) was a subjective experience at age 16 in the author's bedroom: 'my brain overlapping and communicating with another version of myself in a parallel universe.' When the author explained this to a professor during hospitalization, the professor could not understand. The 16-year-old author told the professor: 'You are intellectually limited.' The attending physician at the time (now clinic director) still remembers this event 30 years later. This is the oldest recorded origin of the dual-layer universe concept — preceding the Flickr diagram (2010) by approximately 15 years.
Yoshimitsu Katayama (Thu,) studied this question.