Zin is the Thai lover of Yakuza boss Masashi. Zin was previously the girlfriend of Thai gangster No. 8, who was jealous of her relationship with rival gangster Masashi. After Zin chooses Masashi, he shoots his own toe as a symbolic gesture and forbids Zin from ever seeing him again. Zin asks Masashi to go back to Japan, as they would not be able to be together safely. He begrudgingly leaves.
Soon after, Zin finds herself pregnant and moves into a new place to get away from No. 8. She has a daughter named Zen who is soon found to be autistic. As Zen gets older, Zin one day decides to tell Masashi about his daughter by writing him a letter. No. 8 finds out that Zin is in contact with Masashi and is furious. He visits Zin and cuts off one of her toes to remind her that she is forbidden from seeing Masashi.
Zin is forced to move again to a house shared by a Muay Thai kickboxing school. Zen becomes infatuated with martial arts and from a young age, and learns martial arts by mimicking the moves she sees being performed by the school's students, as well as the martial arts movies that she sees on television, among them Bruce Lee and Tony Jaa films. She also has uncanny reflexes and is able to catch balls thrown at her without even looking. One day when coming home from work, Zin sees a little boy named Moom being picked on in the streets. Feeling sorry for his plight, she takes him in.
Zin then falls ill with cancer and does not have the money to pay for chemotherapy treatments. Zen and Moom attempt to make the money needed to pay for them by having people throw balls at Zen as a street performance act. However, they are not able to earn enough to keep up with the treatments. One day Moom discovers a list of debtors in an old notebook from the days when Zin was a high-interest moneylender under No. 8. In order to get money to pay for her mother's cancer treatment, Zen and Moom decide to collect on the debts. The first attempt to collect the money turns violent, and Zen uses her copied martial arts skills to fight back. This leads to further confrontations with various criminal gangs and, eventually, No. 8.
No. 8 learns that Zen is collecting debts for the sake of Zin's treatment, and Zin finds out what Zen and Moom have been doing for money when her toe is sent to her as a message. She realizes there will be retaliation from No. 8, and sends Moom to mail a letter to Masashi asking for help. Moom is captured by No. 8's gang, but No. 8 has the letter mailed anyway, because he wants to deal with both Zin and Masashi. Masashi receives the letter in Japan and leaves the Yakuza for the sake of his family. When Moom does not return, Zin goes to confront No. 8 to save Moom and try to reach a solution, bringing Zen with her. The meeting turns into a fight in which both Zin and No. 8 are wounded and No. 8 takes Zin hostage.
Zen fights through many of No. 8's crew to get her mother back and faces Thomas, a capoeirista boy with Tourette's who proves to be a match for her until she adapts to his erratic fighting style. Zen's father, Masashi, eventually makes it to the battle, but while he and Zin are fighting No. 8's men Zin is mortally wounded by No. 8. Angered by what has happened, Zen continues to battle through No. 8's men until she catches up with No. 8 and throws him off the third story of a building to his death. She returns to her mother only to find her dead. Masashi comforts his long lost daughter and adopts her.Yanin "Jeeja" Vismistananda as Zen
Hiroshi Abe as Masashi
Pongpat Wachirabunjong as No.8
Taphon Phopwandee as Mangmoom "Moom"
Ammara Siripong as Zin
Dechawut Chuntakaro as Priscilla
Hirokazu "Hero" Sano as Ryo
Sirimongkol Singwangcha as Nak Muaythai
Su Jeong Lim as Su Jeong Lim
Kittitat Kowahagul as Thomas
The star of Chocolate, Yanin Vismitananda, was discovered by director Prachya Pinkaew in 2003 when the director was working on casting sessions for Panna Rittikrai's directorial effort, Born to Fight. Already experienced in taekwondo, Yanin underwent more training with Panna Rittikrai's stunt team. The script for Chocolate was then developed with Yanin in mind. Yanin and b-boying champion Kittitat Kowahagul also trained in capoeira for their fight sequence.
The film was in production during 2006 and 2007, with promotional efforts including a cast appearance at the Bangkok Film Market during the 2007 Bangkok International Film Festival in July. A three-minute promotional video was released online in early January 2008, showing action scenes from the film as well as outtakes of what appeared to be painful injuries for the star and stuntmen.
Critics gave this film a mostly positive reaction.
With the box office success of Chocolate, Sahamongkol Film International was quick to announce their intention to film its sequel (in 3D).