Migi

Migi is the deuteragonist of the anime/manga series Parasyte. He is a parasite who attempted to take over the body of Shinichi Izumi, but was ultimately only able to take over his right hand. Unlike most parasites, Migi didn't develop an urge to eat other humans, due to not consuming the brain of the host, which also allowed Shinichi to retain his individuality. While initially indifferent towards Shinichi, Migi is forced to protect his life in order to survive, as he can't survive without a human host.

He is voiced by Aya Hirano in the Japanese version of the anime and Brittney Karbowski in the English version, the former of whom also voices Haruhi Suzumiya and Lucy Heartfilia.

Appearance
Migi can change his forms depending on the situation, as such he doesn't have a constant appearance. He is also capable of changing his form into weapons such as an arm blade or create human like eyes and a mouth to communicate. As parasites are limited to only being able to mutate the area in the body they merged with, Migi is only able to transform the right arm of Shinichi. Originally Migi's body went all the way to Shinichi's shoulder, but after losing 30% of his body, he now only goes a little past his elbow.

Personality
Migi is a parasite and as such lacks the emotions of a human being. His main purpose is to keep him and his host (Shinichi) alive, even if that means killing his own kind. Due to his curious nature he tends to read a lot, this may imply he is quite intelligent (This is further solidified by the fact he learned Japanese in '1 day' also, Shinichi stated that his right hand was more intelligent than his brain).

Migi often thinks of Shinichi as a threat because he is always getting into fights to save others, and he once threatened to harm him to stop him from getting them in any danger. Due to this cynical nature, Migi will attempt to kill Shinichi's friends if they find out about him.

Throughout the series, it is seen that Migi gains more human-like aspects, sometimes even showing respect towards others, while Shinichi becomes more like him. Migi is also interested in how humans reproduce, asking Shinichi if he can cause an erection in his sexual organ, and even becoming disappointed when Shinichi doesn't have sex with Murano.

Migi considers Shinichi to be his friend and states that he's 'glad he failed to take over his brain'. When Migi visits Shinichi in his dream, before going to sleep for an indefinite amount of time, he thanks Shinichi for all their experiences together and that he was fortunate enough to make a friend.