Susumu Nakoshi is a middle-aged man living in his car. Spending his time between a park full of homeless people and upper-class complex hotel, he is chosen by Manabu Ito to be an experimental guinea pig because he is neither an egocentric wealthy guy, nor a pitiful homeless man. He is "just between".  After the Trepanation he is able to see the "monster" in each human being, things that frighten or obsess people. By studying the human nature and facing the other's fear, he'll try to understand his own person thanks to this strange and worrying 6th sense. When he is stressed or depressed he jerks off and eats his own semen to prove if he is still "alive".

Nakoshi Susumu, age 34, is living out of his car. Between spending his days with the homeless and his nights in his vehicle, he has little to his name–but not so little that he’ll agree to be the subject of a scientific experiment. An unnerving medical student is stalking him and offering to pay Nakoshi a significant sum to test trepanation: the ability to draw out a sixth sense by drilling into the skull. Nakoshi refuses. When Nakoshi’s beloved car is towed, though, he finally agrees to cash and the operating table. At first, the experiment seems to bear no fruit, and Nakoshi’s life is unchanged. That is, until Nakoshi realizes his vision has warped in his left eye…showing him the twisted homunculus inside every human.
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(Source: Seven Seas Entertainment)