Nina Williams was born and raised in Ireland, as was her sister, Anna Williams. From a young age, both were taught various forms of martial arts and other forms of fighting, and a sibling rivalry broiled between the two. Both sisters admired their father, Richard Williams, and they often craved for his attention. Williams was trained in assassination martial arts and borrows concepts from Aikido and bone martial arts, making it ideal for her future job as an assassin. As she quickly became an assassin Williams had later been hired during the King of Iron Fist Tournament to assassinate Heihachi Mishima.
Further information: Tekken 2
Their rivalry catapulting was the part of force that drove them to fight each other later at this time. The other, in Tekken 2, Nina was contracted to kill Kazuya Mishima, but Anna intervened and the conflict prevented her from fulfilling the assignment. She was captured by Mishima after failing to assassinate him and was used as a test subject in the "cold sleep" project by Dr. Boskonovich - a cryogenic experiment. Anna Williams volunteered to be put in cryogenic sleep, but demanded to be awoken at the same time as Nina. Fans speculate about the reason for this. Some believe that Anna couldn't bear life without Nina's presence, some suggest she was envious that Nina would remain youthful in the cryosleep and some think she did it so that she could stay unharmed and ready to fight Nina once she was awakened. The experiments went on for 19 years.
Further information: Tekken 3
Nina had suffered amnesia induced by her years in cryogenic sleep, a fate from which her sister Anna was spared. During Tekken 3, she was controlled by the God of Fighting's spell and while possessed concentrated on killing Jin Kazama - Heihachi Mishima's grandson. Anna worked intensively with Boskonovich to bring her sister's memories back, however, the project was unsuccessful and after a receiving a memory from Tekken 2, Nina realized that she and her sister did not get along. After this, Nina left and does not contact Anna again for some time.
Further information: Tekken 4
In Tekken 4, Nina's experiments had been finished for 2 years and she soon revived her role as an assassin, as it was the only thing that she recalled from her previous life. Her next contract was from the Mafia Syndicate demanding her to kill a British boxer, Steve Fox. As the tournament progressed, she had gained knowledge that she was in fact Steve's mother, who was born through In vitro fertilisation during her years in cryosleep. At the last moment, she abandoned her assassination attempt after detective Lei Wulong brought down the syndicate. After the collapse of her employers, Nina no longer required a viable reason to pursue her target. It was also revealed that she remained emotionally impassive about the discovery of her biological son, but the fact that she did not kill him when the chance presented itself shows otherwise for some
Further information: Tekken 5
Nina decided that it was time she re-discovered her lost memories and came to the conclusion that the only person who could help her was her sister, Anna Williams. Anna meets with Nina soon after. However, Nina's memories and hatred instinctively returned, and they rapidly engaged in a gun battle. The duel lasted for days and the two later agreed to meet at the next tournament and finish their battle. The two promised that only one would walk away from the coming battle, however, Nina refused to take Anna's life as their fight wasn't satisfactory.
Further information: Tekken 6
In Tekken 6, Nina was approached by Jin Kazama to be his personal bodyguard and enters the tournament to intercept any possible threat to him. Anna, during the King of Iron Fist Tournament 5, vows to take revenge and becomes Kazuya Mishima's personal bodyguard, knowing she is bound to come face to face with Nina along the way.