Pinoko is 18 years old and lives with the doctor Black Jack. Well, the origin of Pinoko begins like this, once a celebrity comes to doctor Black Jack for having an operation. She has a big lump in her stomach. At first the doctor rejects the request as the patient's face is covered with some cloth (this is because the celebrity doesn't want to reveal her face).
After some pleadings from her managers, the doctor finally decides to take the case. He finds out that the lump is actually her twin which had not developed completely and had been living inside her since her birth, sharing the same body. Finally the doctor operates and removes the lump and gives her new life by placing her flesh in some child like body (you can say she's half android and half human).
Pinoko is cheerful and lively. She likes the doctor very much, and she always complains to the doctor "Don't treat like a child. I'm 18 yrs old and I'm your wife dammit". She's the doctor's assistant.