Migi

Migi is one of the main characters from Kiseijuu anime and manga.

Migi is the name chosen by the parasite that infested Shinichi Izumi's right hand. Migi is unlike most other parasites in the series. He didn't develop an urge to eat humans, due to not consuming the brain of the host, which also allowed Shinichi to retain his individuality.

Appearance
Migi can change his forms depending on the situation, and therefore 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. He originally infested all the way to his shoulder, but after losing 30% of his body, now only controls slightly past the 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, valuing self-preservation above all else. He also isn't above threatening Shinichi at times, such as when he threatened to gouge out his eyes and ears. 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 his curious nature and the reading it leads to, it can be argued that Migi is quite intelligent. This is further solidified by the fact he learned Japanese in "one day." Shinichi also stated that his right hand was more intelligent than his brain. He is also a capable strategist and can easily think of ways to combat Parasites. Despite, or perhaps because of, his lack of emotions, Migi is very logical and fully capable of listening to reason, and is in fact that one who proposes that he and Shinichi work together in order to survive.

Migi is shown frequently to have a low opinion of humanity. He claims that, out of all life on Earth, humans are the closest things to demons, since humans eat many different kinds of lifeforms in order to survive, while his kind only eats one or two. Shinichi even suspects that he may be right after saving a helpless kitten from a group of thugs, who had buried it in sand and were throwing stones at it. As such, Migi refuses to co-operate with Shinichi to take down Parasites, saying he is an ally to no-one but himself. Due to this cynical nature, Migi frequently warns Shinichi that he will kill his friends if they find out about him.

After fusing himself with Shinichi to save his life, Migi slowly starts to gain 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.

Abilities
Being two separate entities gives Migi and Shinichi a two-on-one advantage in most fights and can allow them to confer with each other to strategize. Migi is shown to be tactical in battle, a characteristic even Shinichi acknowledges. In battle, he tends to measure the strength of the opponent and is shown to be merciless. Migi, like most parasites, is fully capable of transforming into a weapon to fight off other parasites and feels no emotions or remorse in killing his own kind to survive. Migi can harden his body and become muscular, resulting in increased strength and precision of Shinichi's right arm. Through unknown means, Migi has stated that at times, he is able to see, or at the very least feel, the emotions of Shinichi's dreams.

Throughout the series Migi has been shown to shape-shift into various objects and forms, however, the main combat forms include: Migi can use his abilities for other purposes as well. Some of these purposes include: After becoming dormant inside Gotou, Migi gained the ability to think about multiple subjects in various parallel lines of thought. He also revealed that upon his desire, he can become dormant on his own, but is unaware when he'll wake back up.
 * A bladed whip-like appendage.
 * A sword, used by Shinichi whilst Migi was sleeping, as well as by Migi to cut off the head of Miki.
 * A muscular arm, accomplished by adding his own strength to Shinichi's. This form allows Migi and Shinichi to throw a rock around 300 meters with enough power and accuracy to punch a hole in another parasite's chest.
 * Healing Shinichi's heart and wounds.
 * Visual demonstration, i.e. morphing into a gun or flamethrower. It is unlikely that the either is functional, as they require outside entities to fire.
 * Detaching from Shinichi's body to move independently. Both mental and physical capabilities are shown to be diminished, and time of separation is limited unless there is a source of nourishment.
 * Being able to fuse with another parasite's host, and given the chance, rebelling against the controlling parasyte and returning to Shinichi.
 * Migi has shown that he can pick locks, and morph into a key to start a car engine.

Weaknesses
Being a parasite, Migi requires nourishment from the host's body. Unlike others who've taken over the brain, he acquires sustenance from Shinichi's bloodstream. If Migi detaches from Shinichi's body, he starts shriveling up and would soon die. Like all parasites, Migi is weak against fire, causing his surface cells to react in ways that cause functions to fail. Although it is unknown if an actual weakness, it should be noted that Migi has shown discomfort when covered with cold water.

After Migi fused himself with Shinichi's heart, in order to save both their lives, he lost 30% of his original body. This was due to cell loss while making his way back to Shinichi's stump via the blood stream, and thus being unable to recall them due to cells being too small to respond. It's unknown if this caused Migi to become weaker, but it forced him to take on the habit of sleeping suddenly for about 4 hours a day. While asleep, Migi cannot sense anything from the outside world and won't wake up until he has the proper amount of sleep. Once asleep, the signal he emits is weaker than normal, something multiple parasites have made note of. He can, however, shape shift into an object, such as a blade, which will keep its shape even while Migi sleeps.

Trivia

 * Migi makes a hidden appearance in the anime Hunter x Hunter where somebody is reading a manga with Migi on the back.
 * Migi's possession of Shinichi's arm may have been inspired by alien hand syndrome, a neurological disorder that causes hand movement without the person having control over their hand or being aware of what it is doing.