Gintoki Sakata (name based on Kintarō) is a samurai living in an era when samurai are no longer needed. To add to his troubles, oppressive aliens have moved in to invade. Gintoki lives with Kagura and Shinpachi, taking on odd jobs to make the world a better place...and to pay their rent. In the Joi war, he was known as the "White Devil," (Shiroyasha) due to his silver hair and white coat he wore in battle, which, combined with his impressive capabilities as a swordsman, made him famous among his comrades and struck fear into Amanto.

Gintoki has naturally permed silver hair, which he blames for his lacking love-life. He has a big crush on the TV's news weather girl, Ketsuno. In fact, to date, the only time he is seen to have blushed is when he tries to make use of Sadaharu and Ketsuno's dog to get a chance to talk to her. Though several female characters have shown an interest in Gintoki, he usually does not show any response back and merely puts up with them as annoyances.

Gin has two major obsessions in life. His first is a sweet tooth that has him obsess with sugary, sweet foods such as parfait, ice cream, strawberry milk and cake. However, this is a problem in itself in that Gintoki has to control his sugar intake as the doctor has warned that he is on the verge of developing diabetes. His second obsession is reading the manga anthology magazine Weekly Shōnen Jump. (which, not coincidentally, is where Gintama is published in). Gin will go to great lengths to get the latest Jump issue, to the point of reckless behavior leading to situations including an incident of memory-loss and a showdown with fellow Jump obsessee (and skilled ninja) Zenzo Hattori. His Jump obsession makes him easily dream of being like other Jump heroes, including wishing that he had a "Bankai" similar to the hero characters of Bleach.

Despite his appearance and initial behavior, Gintoki has a great amount of pride for the old bushido code. He takes it upon himself to rescue or avenge not only his comrades and friends but also people he barely got acquainted to, be it a pit-fighter who was taking care of abandoned orphans or an Amanto who resembles a kappa. Despite being a fearsome fighter with nearly unmatched skills, he avoids needless bloodshed after suffering the loss of most of his friends and allies during the Joi war.

Kagura is an alien from the "Yato Clan," one of the strongest races in existence. Despite her alien heritage, she looks like a normal human and talks with a Chinese accent. She can stop Gintoki's motor scooter single-handedly and has an umbrella that is bullet-proof and can fire bullets from the tip. Her stomach knows no bounds and she apparently loves to eat sukonbu.
She originally came to Earth to earn money to help her parents' financial situation. Because of her immense strength, she took to fighting for a gang. After she was told to kill a few people, she tried to escape from the gang and was almost run over by Gintoki's motor scooter. He liberated her, and she forced him to let her join his free-lancer business. She sleeps in the closet of Gintoki's home. Kagura has a giant dog-like creature called Sadaharu as a pet, which she had found. Sadaharu has a habit of often biting most characters, with the exception of Kagura.

Shinpachi works under Gintoki to learn the ways of the samurai. However it seems more like he is just trying to help Gintoki pay the rent than to learn. Shinpachi is the captain of the "Otsu Imperial Guard," a pop-singer's fan club.
Shinpachi first met Gintoki after he was tripped by an alien ambassador. Gintoki beats up the ambassador and his guards to get revenge for his spilled parfait. Soon after, Gintoki framed Shinpachi for the crime, which somehow led to him saving Shimura Tae (Otae), Shinpachi's sister, from being added to a brothel.