Hideo Shimada

Hideo Shimada (島田 秀雄, lit. Shimada Hideo) is a parasite with a teenager's body who decides to integrate with human society. He worked with Reiko Tamura to study Shinichi Izumi and Migi.

Appearance
In the manga, Hideo is a young man of slightly above average height, with wide-set shoulders and a generally sturdy build. He has heavily pointed eyes, with wide, flat eyebrows. His hair is neck length and black, with two short bangs at the sides of his forehead.

In the anime, he is slightly smaller, with a lankier build. He had brown hair and light brown eyes. He has a pointed fringe, which spikes down in the middle of his forehead. He wears the same school uniform as Shinichi, which consists of a white shirt and a blue blazer, while in the manga he wears a white shirt with black suit pants.

Personality
When he made his first appearance, Hideo revealed himself to be a relatively peaceful Parasite. After being confronted by Shinichi and Migi, he claimed he had no intention of harming Shinichi or anyone in his school and was more interested in getting to know the two of them.

Despite this, it was revealed that Hideo held no qualms with brutalizing or even killing bullies who tried to start fights with him and continued to hunt humans despite his claims to Shinichi that he was learning to eat normal food instead.

He is an active sports player, and states that it helps him get better at controlling his human host body.

Plot
Hideo is first seen having a conversation with Reiko while feeding on a body. She asks him his body's age, then requests he observe and gather data on a boy named Shinichi Izumi. When he asks the point of all this, she replies that it's for the greater good of their species.

Hideo then enrolls in Shinichi's high school and expresses a desire to become friends with Shinichi, who does not trust him.

Kana Kimishima, following her parasite sense, comes up behind Hideo and mistakes him for Shinichi. This gets his attention and he begins to question her, asking why she thought he was Shinichi when they have little physical resemblance. Shinichi comes across them with Kana trying to escape Hideo's grip, and threatens that if anything happens to the people around them on in their school he will kill Hideo.

After another confrontation with Kana which Mitsuo witnesses and tries to intervene in, Hideo beats up Mitsuo in a bathroom and threatens to kill him next time. Mitsuo is later asked what happened by Yano, the leader of his gang, and the group goes to teach Hideo a lesson. He brings them to a quiet area where he could presumably kill them all without witnesses, but Migi detects his readiness to kill and warns Shinichi, who leaps over a high wall to stop them and inadvertently reveals his superhuman ability to Hideo. Upon being confronted, Hideo allows Shinichi to take care of the gang and leaves.

While watching him, Yuko Tachikawa sees him reform a large dent in his head from being hit by a baseball. Due to her brother's line of work as a police sketch artist, she is peripherally aware of parasites and begins stalking Hideo. After witnessing him morphing his face to entice humans, she later confronts him alone at school. When he tries to attack her she throws paint thinner into his open head cavity and causes him to go out of control. She manages to escape him by leaving through a window and jumping into a tree. Damaged by the paint thinner and unable to change his head back to normal, Hideo's head is stuck in attack mode and he rampages through the school, murdering 17 people. Several policemen attempt to stop him by shooting him, but he is unaffected by the bullets and continues onward. He is eventually killed by Shinichi and Migi on the roof of their school via a rock thrown through the chest, which destroys his heart. His corpse is taken and investigated by Dr. Yui.

Due to his attack, the existence of parasites becomes a widely-spread rumor and paranoia runs rampant in Japan, causing the rate of assaults and suicides to increase. In an effort to curtail this paranoia, the Japanese government spreads a counter-rumor of being able to tell if someone is an impostor by plucking a hair off their head.

Abilities & Powers
Being a parasite, Hideo can shapeshift from the head up and and harden his cells for offensive or defensive purposes, as well as detect other parasite signals and automatically emit his own. He can also maximize the host body's physical potential and disregard pain. During the massacre at the school, Hideo displayed incredible resilience and durability, taking multiple bullet rounds to the body and killing dozens of students and police officers. He only stopped once Shinichi threw a rock completely through his chest to destroy his heart, killing him.

Hideo was aware of humans and their attractions towards each other, using his knowledge to shape his face to looks that would easily entice women into following him.

Weaknesses
Like all parasites, Hideo requires a host body with functioning organs to survive, and would die if he were separated from the body or it was destroyed. Fire can cause his parasite cells to "freak out", making him lose control. He is also susceptible to poisons or caustic chemicals, which would either kill parasite cells on contact or make his host body fail. Due to the paint thinner thrown at him by Yuko, his cells were damaged and lost their morphing capabilities, as well as became divided into smaller, uncontrollable masses that attacked at any sign of movement.

Although he was aware of female humans' physical attraction towards him, he was not always successful at hunting, and had little knowledge or understanding of any relationship between Shinichi and Satomi.

Trivia

 * The name Hideo means "excellence" (秀) (hide) and "male, greatness" (雄) (o).
 * Hideo's surname Shimada means "island" (島) (shima) and "rice field" (田) (da).
 * He is implied to have been working with Takeshi Hirokawa's group before his death.
 * In the live action movie, Hideo's death was roughly similar but Migi turns into a bow and shoots an arrow through Hideo's chest.