Koji Tanaka

Kōji Tanaka (田中 功次, Tanaka Kōji) is an Ajin and the secondary antagonist in ''Ajin. ''He's the lieutenant and the best friend of Sato, after he help him to escape from humans. As the first Ajin discovered in Japan, Koji has been captured by the government and tortured during many years for a experimental and a scientific purpose in order to study Ajins.

History
As the second Ajin discovered in Japan, Tanaka was put into government custody. There, he became a living test subject for various Ajin experimentation by a secret medical facility not known to the public.

After 10 years of being experimented upon, Tanaka is rescued by Satou and escapes the facility. It is assumed the two have been in correspondence since then in pro-Ajin movements across the country.

Appearance
Tanaka is a rather tall man, with a square chin and slightly broad shoulders. He has small, piercing eyes. He has long, slicked back black hair and is often seen wearing a black baseball cap with the letters UCB in them. In the manga, he frequently wears a black leather jacket and olive trousers. In the anime, his black leather jacket is replaced with a red and white jacket instead. He wears a navy shirt underneath. He also wears navy jeans and black shoes.

Personality
Tanaka shows a rather large resentment towards humanity after the daily torture and experiments he was subjected to during his capture. Other than this, he is rather impassive; not really getting frustrated or angry in many situations, and is completely unresponsive to bloodshed and gore.

However, he is shown to care about some people at times, such as the case when he warned two girls about an upcoming terrorist attack as well as helping a woman escape from Satō.

Abilities And Powers
Tanaka has been shown to possess most of the abilities many Ajin possess, as well as some he gained through his capture.
 * Immortality - Tanaka has been shown to have complete immortality, unable to die under any circumstance, including being completely crushed and shot point blank in the head.
 * Paralysis Scream - While he has never been witnessed to use this, it can be assumed that he can paralyse others around him by screaming, as it is a basic trait amongst Ajin. As explained, by screaming, any person around him will be completely immobilized by a certain period of time, however this loses its effectiveness somewhat if the person is aware that the user is an Ajin, or has ear protection.
 * Immense tolerance to pain - Due to his capture by the government and his daily torture, Tanaka has developed an extremely high pain tolerance.
 * IBM - Tanaka has been seen to use an ability possessed by many Ajin, the power to produce a strange invisible matter that can form into a Black Ghost, or IBM, as the government refers to them. Tanaka's ghost is fairly basic in its appearance, with a rounded, dome-like head, and a thin body that looks like it is composed of bandages. It has extremely sharp claws capable of cutting flesh, bone, and even other ghosts with ease (although Black Ghosts are unable to be destroyed by cutting blows), as well as sharp teeth that have not been incorporated in combat thus far. It is extremely limber, able to attach itself to walls and "bounce" between foes in combat with lethal effectiveness.

Trivia

 * There is a running gag in the series on how he's bad at shooting, with Satō mentioning it several times.
 * There is a bit of an inconsistency about his time being captured. It is said that he is the second discovered Ajin in Japan, the first being Shinya Nakamura. He gets captured and gets subjected to torture for the next ten years. Izumi Shimomura is taken as a bodyguard to Tosaki 19 months after the Shinya Nakamura incident, and she is twenty years old at the time. If Tanaka really got captured for ten years, this would make both Shinya and Izumi at least in their thirties, which doesn't seem very probable.