Susumu Nakoshi, a middle-aged man dividing his time between a luxurious hotel and a park inhabited by the homeless, encounters a peculiar young man seeking volunteers for trepanation—the act of drilling a hole in one's skull. This enigmatic individual, deeming Nakoshi the ideal candidate, initially faces rejection but later reconsiders after a mishap with his towed car. In a deal for 700,000 yen, Nakoshi consents to have Manabu Ito, a 22-year-old medical student, perform the procedure. Initially, no changes manifest in Nakoshi post-operation. However, his reality takes a bizarre turn as he starts perceiving homunculi in every person he encounters. With his perception altered, Nakoshi must navigate this newfound vision of the world.