Shinichi Izumi is the main character in the manga and anime series "Parasyte." Initially an introverted high school student, his life changes dramatically when he forms a unique partnership with a parasitic alien entity named Migi. Throughout the series, Shinichi evolves from a timid teenager into a more assertive and resourceful individual, all while navigating the complex world of parasites, moral dilemmas, and human nature. His character development is a central theme in the story.