Homunculus is a psychological thriller film based on the popular manga series by Hideo Yamamoto. The movie centers around a disheveled and homeless man named Susumu Nakoshi, who is approached by a medical student named Manabu Ito with an unusual request. Manabu, who is struggling to come up with a thesis topic for his medical research, offers Susumu money in exchange for allowing him to conduct a trepanation procedure on his skull.
Despite being skeptical of Manabu's proposal, Susumu agrees to the procedure, hoping to use the money to start a new life. Much to their surprise, the procedure turns out to be successful, and Susumu develops a mysterious ability to look inside people's minds and uncover their deepest, darkest secrets.
As Susumu struggles to come to terms with his newfound power, he realizes that it comes with unintended consequences. He becomes embroiled in a string of crimes, as his ability leads him into the twisted and corrupt world of Japan's underworld. He also becomes the subject of many experiments, as researchers try to figure out what makes him so unique.
Throughout the movie, Susumu battles with his inner demons as he tries to balance his new life with his past. As he delves deeper into the minds of the people around him, he discovers that no one is truly what they seem, and everyone has their own secrets to hide.
Homunculus is a thrilling exploration of the human mind, and the twisted forces that drive us all. The movie is a dark and thought-provoking journey that will leave audiences questioning their own thoughts and beliefs.