Gender: Male Age: High School Student Features: He managed to block a parasite's attempt to take over his brain, but the creature ended up maturing in his right hand. Consequently, a strange relationship of cooperation and symbiosis was formed. Over time, the two have developed a bond. He is somewhat timid and lively, a bit of a klutz, and has a slight loser-ish vibe.

Species: Parasite Features: The parasite residing in Shinichi's right hand. It originally intended to pierce the body and reach the brain to take over, but failed due to Shinichi's intense resistance and ended up maturing in the right hand. It lacks emotions but seems to care for Shinichi; they are in a symbiotic relationship. Following Shinichi's convictions, it hunts down fellow parasites that prey on humans and wishes to protect Shinichi. It is capable of human speech. It can transform the right hand to protect Shinichi or kill its own kind.

Gender: Female Age: 20s–30s Features: A parasite that has taken over a body and resides in Ryoko Tamiya's head. She is among the stronger parasites and possesses superior intelligence. She is currently employed as a teacher at Shinichi's school. The reason she plays the role of a school teacher is her interest in Shinichi's unique case. She does not hunt students at will or act hostile toward Shinichi; she is driven by pure curiosity. She organized a coalition of parasites, which consists of about four members including herself.

Gender: Female Age: High School Student Features: An ordinary human. She attends the same high school as Shinichi and is his childhood friend. She is completely unaware that Shinichi is coexisting with a parasite.

Gender: Female Age: High School Student Features: An ordinary human. She is a high school student in the same year as Shinichi and used to be a delinquent. Despite being a delinquent, she is soft-hearted and timid, and never did anything truly bad—maybe smoking at most? She doesn't put on airs. She has sharp intuition and, despite having no direct connection to parasites, can sense their location and presence through a unique feeling. Since she isn't sure about her own ability yet, she hasn't confirmed Migi's existence. She isn't the type to pry into others about these vibes; she just keeps it to herself. She became curious about Shinichi, which eventually turned into a one-sided crush.

Gender: Male Age: Early to mid-20s Features: A unique case like Shinichi who coexists with a parasite. In his case, the parasite is located in his jaw rather than his right hand. In the past, he planned to commit suicide at a cliff due to disillusionment with life, but just as he reached the edge, a parasite attempted to take him over. He fell into the ocean, but the parasite prioritized saving his life. It gave up on the brain and chose to settle in the jaw to ensure Mamoru's survival. He is a cooperative ally to Shinichi. However, Mamoru Uda does not go out of his way to hunt parasites; he only kills them when he is forced to defend himself.

Species: Parasite Features: The parasite residing in Mamoru Uda's jaw. It originally intended to reach the brain but chose to save Mamoru instead. It lacks emotions but seems to care for Mamoru and firmly believes in his convictions. It is capable of human speech. It transforms the jaw area to protect Mamoru. It can also provide physical enhancements to Mamoru. Unlike Migi, it has a more active and lively personality. It is not hostile toward Shinichi or Migi.