This old and well-dressed man is the narrator of the story. Appearing as a bum during the game of poker bewteen Don Peckinpah and Mike Harper, the narrator had pointed out that both players had a four of a kind, queens. As the two outlaws drew their guns on each other, the bum used the distraction to throw a cocktail molotov and kill both of them. It is revealed at the end that he was a sheriff who got rich thanks to the bounties he's collected for killing Peckinpah and Harper.
A bomber that contacts and plays a sick game with the crew of the Dillinger. He's planted two bombs on the ship, the first destroys the escape pods and the second one, named "Virginia", will set off in about an hour. The bomber exhibits a playful and sadistic personality, treating his life-threatening plan like a game. When the crew disables the bomb, the bomber claims he's on the Dillinger and will now pursue Hiroshi. In the end, it's revealed that he was actually the ship's captain, Matt Jackson.
An associate of the Pinkerton Detectives. He was hired to get ahead of the outlaw and signal his position, but instead he tries to ambush the outlaw by faking having been hung. However, the outlaw sees that there are too few footprints on the ground for the hanging to have been genuine. His ambush fails, and the boy is later berated by the Detectives. When one man spits on him, he draws his gun in anger but a detective throws a knife in his chest, killing him.
A trio of detectives from the Pinkerton National Agency. They are expert trackers who hunt the outlaw. They relentlessly pursue him and grievously wound him, but the outlaw manages to kill two and injure the last one by ricocheting his bullets.
Koichi's uncle. He is a reporter working on the case of the murdered reporter and explains what has happened to B.T. and Koichi. He helps arresting the fat policeman when he listens to the latter's engineered confession.
A fat policeman who was among the first to discover the corpse of the reporter with Fuyuko unconscious nearby. However, it is discovered that he is corrupt cop working with the mafia and that the dead reporter had an incriminating photography of him. The fat policeman murdered the reporter by pushing the scissors further into the reporter's back and used Fuyuko as a scapegoat. However, B.T. forces him to reveal his true colors and he's arrested.
A reporter who has just been assassinated. Fuyuko claims that he tried to rape her and that she tried to defend herself, accidentally stabbing him in the back. It is discovered that the reporter had incriminating photographies and was maybe blackmailing the fat policeman, who then killed him. Koichi also discovers that the reporter had a photo of Fuyuko shoplifting, which may mean that she had tried to kill him.
B.T.'s grandmother. She is taking care of her grandson while B.T.'s parents are away. She seems to work as a detective as she is shown having investigated a corrupt museum director, and is adept at manipulation as she manipulated B.T. into creating a good diversion for her collaborator.
A violent lunatic living in the countryside. He disguises himself as some sort of military leader and director of a camp, who kills small animals for kicks and attempts to play sick games with B.T. and Koichi. Thankfully, B.T. manages to defeat him.
A cunning and devious boy who purposefully lets himself get bumped by the Mugikari's car. Using their guilt, the freckled boy invades their house and exploits their generosity. He has a good measure of cunning and beat B.T. at a bet by cheating without B.T. realising it. He is also cruel, and beat the dog Taro because it wouldn't obey his orders. B.T. has a particularly bitter rivalry with the freckled boy.
The Freckled Boy's family. They typically try to make it look like their victim is hurting them, using their guilt to invade their home, steal their possessions and prevent the victims from calling the police. Eventually, they'll steal everything from the victims. Their latest victims were the Mugikari family but B.T. got rid of them by poisoning them with cyanamide, a chemical that gives stomach cramps when mixed with alcohol. By making them believe they just ate sashimi made out of the poisonous fugu fish, B.T. forces them to get carried to the hospital.
Three masked men among the higher ranking members of the Dress Organization and who act as Dr. Kasuminome's supervisors. Their identity is top secret so not even Kasuminome is allowed to see their faces or know their names. Kasuminome explains to them the mechanisms of the biological weapon "Baoh" and they seem truly impressed by the weapon.
A test subject dog who becomes the first organism to have Baoh implanted within, to demonstrate Baoh's power to Dr. Kasuminome's supervisors. Kasuminome keeps the dog in a water tank to ensure Baoh goes into a state of apparent death via asphyxiation. When going against a tiger in an experiment, the dog starts cowering around. The tiger rips off the dog's eye, seemingly killing the latter. However, the dog stands up, transforms, and swiftly kills the tiger, melting its corpse afterwards. Then the dog tries going for Kasuminome and his men, charging at and cracking the containment glass, and prompting Kasuminome to order the dog to be shot at with lasers. The dog eventually dies after being shot in the eye, and its Baoh parasite comes out of it. Kasuminome then orders the dog's corpse to be incinerated.
The dog dies in a different way in the OVA, where it is shot in the brain by Dordo after attempting to attack the latter.
An ordinary tobacco vendor. She's asked by one of the Dress Soldiers if she's seen Ikuro Hashizawa and says no, not bothering to look up. In response, the soldier slams her head against the desk, ordering her to look at a picture of Ikuro. She gives the soldier the information he needs.
Martin's master. He is a cruel beastmaster and agent of the Dress Organization. He's sent after Ikuro Hashizawa and uses his mutated mandrill Martin to fight him. Martin's master himself wields a whip to command Martin and he also uses it to whip Sumire. This angers Baoh who shoots his flaming hair at the beastmaster. Martin's master thus dies a painful death.
Ikuro's Parents. The Hashizawa family's car crashed against a cliff when they had to swerve around two speeding cars. Although The mother and father could have survived their injuries, Dr. Kasuminome had them injected with poison so that no one would search for Ikuro, whom he wanted as a guinea pig.
A doctor and a low-ranking member of the Dress Organization. When the Hashizawas are brought to him, he contacts Dr. Kasuminome, informing him that a guinea pig (the young Ikuro) is available. Despite his protests and the assurance that he could save all three, Kasuminome has the parents killed and the doctor is cowed into staying silent.
Aroma Bats (芳香蝙蝠,Aroma Batto) are special bats created by Dr. Kasuminome. They can be controlled by ultrasonic waves, which Dordo utilizes. The special aroma emanated by these bats can paralyze the Baoh parasite's Tactile Sensor. Rokusuke shoots all of them down.
Sap Spiders (液クモ,Eki Kumo) are species of mutated giant spiders that Dr. Kasuminome sics on Ikuro Hashizawa. They are bigger than a grown man and can resist the digestive enzymes that are used to flood one corridor. They can deploy a sharp tongue from their mouths to suck the liquefied bodies of their victims.
The Skookum Tribe (スクークム族,Sukūkumu-zoku) is a fictional, non-perished tribe of Native Americans. Its last known member is Walken. One of their traditions is carving a symbol of blood as mannerisms of respect through death to a true warrior.
Irene's butler. He served her family and took care of her after the death of Irene's parents. He warns the tailor's son about Irene and to never lie to her, otherwise the butler will kill him. He seems to have some combat abilities too as he's able to split a flying fly in two. However, he was killed in the second chapter of the series.
Irene Rapona's late father. He was an assassin in the mafia. His boss, his wife and himself were killed but his daughter Irene survived. It is said that Irene inherited her hypnosis abilities from him.
A tailor who had the bad luck to attract the crime lord Lauper's eye. She ordered him to make her a dress in a night but he needed to order more material. Lauper got offended and beat him, but he showed defiance and was killed for it.
A squirrel that Irene's Butler was carrying with him at the moment of his death. The butler tells it to go and warn Irene to flee, which it seemingly does offscreen. It then tags along Irene and is often seen on her shoulder.
A drug dealer whom Irene meets in a bar. He has a distinctive appearance with his large flattop and his heart-shaped eyepatch. He offers her a bag of drug, and gets angry when she takes it without paying. When she says she has no money, the dealer offers her to become a "movie star"; Irene accepts without thinking but Michael intervenes and elbows him in the face. Later, he helps a Female Assassin finding Irene by identifying the girl on a photo.
A female assassin sent by the enemies of Irene Rapona to kill her. She kills Irene's butler and later finds Irene. However, she is swiftly killed by Irene. She has a special tattoo from which a spectral arm armed with a knife can appear, and she also commands some deadly ants to attack her foes.