Pinoko is Black Jack's sidekick and she usually claims to be his wife (which she is not). Despite her appearance, she is actually (mentally) eighteen years old even though she has the body of a toddler. She was originally a "teratoid cystoma" (despite not being an actual medical term, she is most likely a teratoma. A teratoma is a tumor made up of several different types of tissue, such as hair, muscle, or bone. They typically form in the ovaries, testicles, or tailbone and less commonly in other areas) growing on the side of an eighteen year old girl. She was then detached and her already developed body parts (she had supposedly developed a brain and an entire nervous system with a variety of organs) were transplanted into a synthetic body. Thus, she is cursed to never be able to grow, despite her only wish is to grow up and marry Black Jack. She is known for her famous catchphrase, "acchonburike", which has been translated as "oh my goodness" or "ohmigewdness" in some English adaptions, but is devoid of any real meaning.
It is said that Pinoko is loyal, practical and orderly. She helps with chores around the house and sometimes helps Black Jack in surgeries whenever she can. Despite this, it is easy to get her angry and is very susceptible to anyone who calls her a 'girl' and generally responds with anger claiming that she is eighteen, "and a lady". Although she tries her best to play the part of a lady-like housewife, she ends up being more of Black Jack's daughter. She shows extreme concern for Black Jack, and will stay by his side regardless of the situation (whether or not Black Jack wants her there). She also develops a huge crush on Black Jack, which is shown throughout the manga and anime. She even claims that she is his wife, even though these feelings are never reciprocated (Black Jack never shows any romantic feelings for Pinoko and he just shows a kind of fatherly love for her). When Black Jack is around other women, she gets very alert and starts asking bothersome questions and/or attacking the women he's with (trying her best to kick their shins or something rather mild). Although she is often portrayed as a disobedient child, Pinoko shows a good emotional contrast with the more "stoic" Black Jack. Sometimes, she is emotional support in moments of anguish and sometimes it has given the doctor something to worry about, and at times of danger, a will to live.
Pinoko began life on her twin sister's abdomen as a teratogenous cystoma (see top of page. Also, keep in mind this is a fictional series. All medical information may not be accurate). Since then, Pinoko started to develop as a tumor on her twin sister's abdomen and "lived" there for eighteen years. Although, she began to develop over a span of eighteen years and eventually developed an entire brain, complete nervous system, and random organs and limbs. Soon, the tumor was so large it had to be removed due it being so large. It was then separated by Black Jack in an operation. Before the doctors consulted Black Jack to proceed with the removal of the tumor, previous surgeons found it hard to operate on the twin sister due to a sort of curse cast on them when attempting to operate. Supposedly, all of those attempting to operate on the tumor (which was Pinoko at the time) all had a frantic fit, and began to harm themselves and destroy various pieces of medical equipment. The surgery constantly had to be cancelled due to this problem and the doctors had no choice but to seek Black Jack's help in order to remove the tumor.
During the surgery, Pinoko began to enact the supposed "tumour's curse" as she did to the previous surgeons. (She is somehow able to telepathically communicate with and control the surgeons. This is how she enacted the supposed "tumor's curse". After she is extracted, she is no longer able to control people or communicate telepathically.) She almost forces Black Jack to shove a scalpel into his throat during the operation until Black Jack attempts to bargain with her by saying that he will promise to keep her alive once she is removed from her twin sister's body. After agreeing with Black Jack, she lets him proceed with the surgery without disturbance and was kept inside a culture medium for some time after the removal. While her twin sister is taken back to the hospital, one of the doctors is horrified when they see the tumor being kept inside the culture medium. He frantically asks Black Jack to throw it away but Black Jack refuses to do so saying that it is up to him to do what he wants with the remaining body parts. After they leave, Black Jack immediately begins with another surgery on the remaining parts, assembling and arranging the scrambled body parts into a complete body. The body has the appearance of a toddler, and is partially made of synthetic materials and the organic bits left over from the operation (This is essentially Pinoko at the time). The body is soon connected to the brain, Pinoko's brain, and body. Pinoko's body is placed in a bed, and she soon gains consciousness. She is barely able to babble in her new body, and is technically nameless at the time. But, Black Jack soon takes inspiration from an old fairytale book lying on his table near Pinoko. It is the tale of Pinocchio, the wooden puppet who becomes a real boy. He then names the girl Pinoko. This is how Pinoko is "born".
While it's not shown in the manga, the anime depicts Pinoko's attempts at getting used to having her own body. Throughout the process, Black Jack refuses to help, as he himself had to recover from his own operation as a child on his own. He believes that the struggle he went through was a valuable experience for him as a person, and believes Pinoko should learn this lesson. This may be because she is in a similar place as him earlier in life, and must learn to cope with her physical debilitation. Pinoko spends her days learning to walk and maneuver her new body. Later that night, there is a fire in Pinoko's room. Pinoko manages to pull herself together, and get up and walk just in time to escape the fire. This experience helps her learn to walk and properly make sounds. She then trains herself to become a "normal" human without Black Jack's help and quickly adapts to her new body, able to walk, run, talk and much else; Even becoming a sort of house wife while still going to preschool, and dealing with any number of medical emergencies she may have to deal with.
A year after Pinoko and her twin sisters separation, the doctors brought Pinoko's sister back for the final checkup. Before leaving, Black Jack tries to introduce Pinoko to her twin sister, where in a comical fashion, Pinoko begins to attack her sister by jumping up and down on her while calling her various names. She was angry at the multiple attempts by her twin sister and many others to get rid of her, causing her to hate her sister and to trust only Black Jack. Her sister then angrily announces that she disowns her and leaves in a hurry with the other doctors. However, this is changed in the 2004 TV anime, mainly targeted towards children, and she is shown talking to her twin sister but she gets immediately rejected as her twin sister simply states that she has no sister. Pinoko is immediately infuriated by this and begins to attack her sister in the original comical style as the manga. The twin sister quickly leaves the house, leaving Black Jack and Pinoko behind. Since that day, Pinoko became Black Jack's assistant and adoptive daughter. She still holds a grudge toward her twin sister to this day.
Pinoko has short orange hair, that is also sometimes depicted as either a reddish ginger or a chocolate brown. She also has a pair of brown eyes and a light complexion. She is the height and weight of the average toddler since she is physically unable to grow normally due to her synthetic body. Her hair is a rounded bob cut, and she wears four pink bows on the of her head, red overalls with a frilly skirt trim, and a yellow long sleeve shirt. She also wears a pair of white knee high socks and tiny red strap shoes.
- Her twin sister's name is Yurie as mentioned in Black Jack Final OVA but was usually nameless in the manga and anime series. Her face was never shown in the anime series as she wears a mask all the time.
- Pinoko's synthetic body was inspired by a young girl who used to be a model. Black Jack mentioned he chose her as a model for the body because he thinks she looks rather cute (take note that Black Jack has no romantic ties to anything about either of these girls). This plot point is reminiscent of Dororo, another manga by Osamu Tezuka, in which the main character has extreme body enhancement and replacements, to the point he is more synthetic that organic.
- Due to her synthetic body, Pinoko has some disability. This affects her ability to swim and grow. Although this is not because of her synthetic body, Pinoko has a heavy lisp that is present in the manga and anime. She has a lisp simply because she doesn’t put any effort into improving her speech.
- Pinoko is technically zero years old as stated in her birth certificate, but she is mentally eighteen since she grew together with her twin sister on her abdomen for eighteen years.