Migi is a unique type of Parasite that resides within Shinichis body. Unlike typical Parasites, Migi does not require human blood for survival and instead feeds off the food that Shinichi consumes. Unlike other Parasites, Migi lacks emotions and prioritizes his own survival above all else. He has threatened to harm others who pose a threat to him and Shinichi's safety, even going so far as to attempt to remove Shinichis limbs in order to prevent them from putting themselves in danger. Despite this, Migi is capable of being reasoned with and shares Shinichis mistrust towards other Parasites. Unlike Shinichi, however, Migi has no inclination to put himself at risk to protect others from the dangers posed by Parasites.
By the end of the series, Migi has stated that he will go into dormancy, due to the amount of information he gained from Goto, he wishes to contemplat
As the series goes along, however, he becomes more human, whereas the reverse happens to Shinichi.