Koichi (Takeru Sato) & Atsumi (Haruka Ayase) have been friends since their childhood days and they eventually became lovers. About one year ago, Atsumi attempted to commit suicide and fell into a coma afterwards. Koich, desperate to know why Atsumi attempted suicide, takes part in a new medical procedure that involves the central nervous system. Koichi will enter the subconscious mind of Atsumi through the medical procedure.
When Koichi enters the subconscious read moremind of Atsumi, shes asks Koichi to find a picture of a "plesiosaur" she drew as a child. The drawing is the key that brings back a suppressed childhood memory that brings their minds together.