Manabu is a cunning and devious boy who purposefully lets himself get bumped by the Mugikari Family's car. Using their guilt, the freckled boy invades their house and exploits their generosity. B.T. develops a particularly bitter rivalry with him.
Manabu is a little boy with an average constitution, and a round face. He seems to be the same size as Koichi Mugikari. He's got unkempt dark hair. He notably has freckles in the middle of his face and puffy hair. He also happens to be missing several front teeth.
Manabu appears wearing a checked shirt in a diamond pattern and rolled up pants. He also doesn't wear shoes. Later he steals Koichi's clothes and wears a trucker jacket with two breast pockets, a white shirt and plain pants with a belt.
Cool Shock Old B.T.
In the Cool Shock Old B.T. one-shots set decades after the original series, Manabu has become an old man who is lean and a little smaller than B.T.. He is now bald with several wrinkles. Manabu still wears a trucker jacket but under it wears a shirt with a double circle motif, and a pearl necklace. His pants have an arrow motif imprinted on them, as do his shoes who have black and white arrows imprinted under the soles. Manabu now wears round glasses and walks with the help of a cane, which hides a sword inside.
In Cool Shock Old B.T. Chapter 2: The "Say Hi to Old Virginia" Incident he now has a completely steel-platted body and robotic body covered in circles appearing to be bolts, and is wearing a high-collared jacket that appears to be made of metal too. He has two small tubes going from the back of his head to his jacket, and two more larger tubes protuding from behind his jacket seemingly attaching him to his spaceship.
Manabu is a devious, greedy and violent boy who revels in exploiting others.
When he appears, the freckled boy seems to be innocent and reasonable, although he shows an unusual high level of familiarity. As Koichi's parents try to get on his good side by welcoming him inside of their home, he quickly abuses their hospitality, from sleeping on the couch immediately after going in to devouring a large part of the family's dinner while complaining about the meat being too salty to Koichi's mother. He then steals Koichi's clothes for himself. In general, Manabu has a cheerful and friendly behavior but it is only an act in order to approach his victims.
Manabu's unpleasant behavior can be explained by the fact that he comes from a family of hustlers. Manabu cheerfully claims that they routinely infiltrate households, probably using Manabu as bait to catch the victims unaware and frightful of the consequences of having run over a boy. The family then uses the opportunity to force themselves inside of a house, intimidating the victims by playing the victims themselves, overreacting and pretending that the victims are assaulting them. This leaves the victims unable to do anything for fear of the police believing the story of Manabu's family. Manabu also happily says that he and his family will dispossess the Mugakari of their possessions, threatening to leave them bankrupt, and gloats that his family will do so forever.
Manabu is also quite violent. When he manages to acquire Taro, Koichi's dog, Manabu tries to force Taro to do tricks for him and beats him with a tree branch when the dogs disobey, getting angry at the dog for "being lazy". When B.T. poisons his family and forces them out, Manabu also tries to get his revenge by attacking B.T. with a knife, though he misses his throw.
Manabu is a big eater, capable of devouring a whole picnic and drinking a whole one liter bottle of soda in one gulp. He mentions loving onigiri.
He likes playing mind games and making bets with people, which is another way for him to con people. For instance, he challenges B.T. and Koichi at seeing whose candy will reach an ant colony first, but he also had secretly sprayed the area with insect repellent beforehand to guarantee his win. This allows him to win Koichi's dog. Later, Manabu challenges B.T. to trace a special grid without lifting the pen or going over anything once. Once he's defeated, he reluctantly acknowledges B.T.'s own cleverness after realizing he got baited into being run over by an ambulance.
Manabu is a fairly intelligent and devious boy, coming from a family of hustlers and thus having an affinity with hustling, manipulation and cheating.
He demonstrates a good deal of cunning and is the only opponent in the series to beat B.T. in a battle of wits. By preemptively cheating and making B.T. drop his guard to bait him into a bet he was sure to lose. Likewise, Manabu seems to act as bait on a regular basis to help his family take over households through acting and deception, playing the victims so that the real victims feel they can't call the police for help.
- Butterfly knife: Manabu possesses a butterfly knife which he uses once, throwing it at B.T. However, he misses.
- Sword Cane: In the spin-off Cool Shock Old B.T., Manabu now possesses a sword cane. He charges toward B.T. with it but the sword misses B.T. and punctures his vintage car's tire instead after Manabu is hit by a car.
Cool Shock B.T.
Not much is known about Manabu before his encounter with B.T., as Koichi comments on the mystery around the boy's age, upbringing, and school. His close family is made up of 6 people total including himself, appearing very close to one another as they assist each other in their deceit.
Manabu is first introduced in the story pretending to be the victim of an accident caused by Koichi's father while pulling out of their driveway. Worried about the boy's "injured" state, they bring him into their home, letting him rest and offering to take him to the hospital to which he declines. Once he's entered and secured the house, Manabu naps for several hours.
Upon waking up, he immediately intrudes on the family's meal and invites himself to join them, sloppily eating through most of their food, harassing Koichi's mother over the quality of the onigiri, and breaking the family's teapot. After hastily finishing the meal, Manabu receives a phone call from his mother, to which he tells her all the great things about the house he's staying in before abruptly ending the call with no mention of returning home anytime soon. Later in the day, Manabu steals Koichi's clothes, now sporting a denim jacket and pants, white shirt, and belt. Continuing to forage through the family's fridge with no regard for asking permission, he continues to rile up and aggravate B.T., to whom he stares down smugly.
Meeting B.T. and Koichi outside playing with their dog, Manabu sets up a rigged bet between himself and B.T., the prize being the very dog they've been playing with. The game is to see which piece of candy (offered by Manabu) a nearby colony of ants will go to first when placed 30 cm from the entrance of the anthill. Before the game even began, however, Manabu made sure to spray insect repellent around the area where he predicted B.T. would place his piece of candy, rendering any strategy futile. Winning the bet, Manabu gains ownership of Koichi's dog.
After an undisclosed amount of time between Manabu winning the bet and the group entering the house again, the Mugikari family is met by a sudden ring at the doorbell. Manabu runs to the door to open it and the rest of his close family is revealed as they invade the house as well. When B.T. visits Koichi the next morning, Manabu and his family are still at the home, having stayed the entire night. Outside the home, Manabu continued to torment and abuse Koichi's dog, finally revealing the master plan of the family, to claim ownership of the Mugikari home and all of their belongings for themselves.
Later that evening after stumbling upon his family eating the dinner B.T. made for them, Manabu is told that the dinner his family consumed is poisonous blowfish, followed by his family getting incredibly sick all of a sudden and passing out onto the floor. Manabu calls B.T. a murderer and chases after him while his family is being loaded into an ambulance. Finally finding B.T. after following the sound of his whistle, Manabu pulls out his knife, ready to throw it at B.T., before he is suddenly hit by the same ambulance that came to pick up his parents. His dagger misses B.T. and he coyly reveals to Manabu that he never fed his family blowfish to begin with, and that he simply mixed in some cyanamide into the meal. While being driven to the hospital, Manabu comments on B.T.'s undeniable cleverness with a seeming sense of respect.
At some point, Manabu becomes the boss of an organization called "The Outlaw Guys". Disguising themselves as an investment company, The Outlaw Guys scams the elderly to steal their property and income. Manabu hires young adults to work for him, referring to them as his slaves. One day he blackmails an elderly lady from a candy store by mentioning that her reputable grandson may have knocked up a teenage girl, so she runs around collecting money for him so he doesn't spread the rumor.
Sixty years after Manabu harassed Koichi's family, his employees target a 72-year-old Koichi, selling him a run-down house which they advertised as a 70-million-yen villa and stealing his current property and life savings. While Manabu's staff continues scamming the elderly, one of them remarks how seniors can be so stupid and gullible. In response, Manabu angrily tells his workers not to insult the elderly and to scam them respectfully. One of his employees then points out a video on J-Tube showing Koichi discussing how he found rare jewels in the furniture of the new house he bought and is now a millionaire. Thinking the two employees who scammed Koichi messed up by leaving the jewels there, Manabu punishes them by stepping on them and kicking them. He orders them to go back to Koichi and get the house and furniture back from him.
While the two take a long time before coming back to Manabu's hideout, Manabu reads a novel that Koichi wrote when he was younger called Cool Shock B.T. He suddenly realizes that the video must have been a ploy and declares to his gang that they have two minutes before they must evacuate the place. Before they could all leave, B.T. crashes into the building with his car. The boss declares that he knew they would try to hit him with a car again, since B.T. did with an ambulance 60 years ago. However, B.T. doesn't recognize him. Manabu reveals that he already sold Koichi's house for seven million yen. He offers B.T. to make a bet. If he loses, he'll buy the house back since he still has the contract, and if he wins then he'll take B.T.'s vintage car. B.T. accepts and Manabu explains the rules. He reveals a pouch full of coins and says they'll gamble by scattering all the coins across the slanted tables, with the winner having to guess whether there will be more heads or tails. B.T. says he's fine with the game but would like to change the rules. He suggests that they decide the winner based on whether the difference between heads and tails will be an odd or even number. Manabu agrees and chooses that it'll be even, so B.T. goes with odd.
Koichi is the dealer and tosses the coins as the game begins. Koichi notices that B.T. was palming a coin that he pickpocketed. If he placed an extra coin on the table, B.T. could ensure the difference would be an odd number. However, Manabu also had a coin hidden in his palm. Manabu notices B.T. move his hand so he also places his hidden coin on the table in order to make it an even number. He declares that he's the winner and laughs until he notices that it's actually an odd number. Dumbfounded at his loss, Manabu unsheathes his cane to reveal a sword and charges toward B.T. However, B.T. had hacked the autonomous car of the scammers beforehand and set it to target Manabu. Manabu is hit by the car and his sword goes flying, landing beside B.T. and puncturing his vintage car's tire. B.T. uses the autonomous car to send Manabu and his slaves to the police hospital. Tied up to the car seat, Manabu declares that they'll meet again someday.
In the year 2060, B.T. and Koichi Mugikari board a spaceship and travel into space.
Manabu hatches a plan to kill them both. Manabu smuggles two bombs into B.T.'s spaceship. The first, smaller "vacuum bomb" is placed near the escape pod and he adds in a puzzle in the form of a shogi set piece. With this puzzle, Manabu plans to pique B.T.'s interest and make him lose time. He smuggles in a second bigger bomb which he places in the engine room and this one has no way to be disabled.
When B.T. and Koichi fly into space, Manabu follows them aboard his own private spaceship. He then contacts Koichi while hiding his identity and reveals the existence of the bombs. Waiting a moment before parking next to B.T.'s ship, Manabu recontacts the ship just to enjoy the despair of his foe. Gloating, Manabu wants to warp into the ship to become B.T.'s master once he yields. However, B.T. has already disarmed both bombs. Plus, B.T. hacks Manabu's ship and redirects it into the path of an asteroid. It presumably crashes into Manabu's ship but B.T. expects Manabu to survive this ordeal as well.