Homunculus centers on Susumu Nakoshi, a 34-year-old homeless man living out of his car, who is accosted by a stranger to have an experimental surgery known as trepanation (drilling a hole in the skull to increase circulation that supposedly brings out a person’s ‘sixth sense’ and allows them to see ghosts and use ESP). Following the surgery, he begins to see distortions in the real world through his left eye.