Nina Williams (ニーナ・ウィリアムズ Nīna Wiriamuzu?) is an Irish, cold-blooded assassin that made her first appearance in the original Tekken game and has appeared in every Tekken game ever since. Nina has a lethal fighting style, consisting of throws, grapples, and holds. She has a rivalry with her younger sister, Anna Williams. During the end of Tekken 2, both Nina and Anna undergo Cryogenic Sleep. They are experimented upon for 15 years (this is the reason why they both remain physically young throughout the tournaments).

While in Cryogenic sleep, her ovum was taken without her consent and used to create Steve Fox (who first appears in Tekken 4 and onwards). Nina also starred in her own game, Death by Degrees, an action-adventure title released in 2005 for the PlayStation 2. Nina and her younger sister both come from the island of Ireland. It is not specified if she comes from Northern Ireland, or the Republic of Ireland. Nina's persona seems to be cold and indifferent. In fact, she had been drugged by an underground force when she was young in order to create the perfect assassin, regarding the chronology of Death by Degrees.

Her bitterness and hatred towards men could be a result of her defilation after Tekken 2. The only man she had ever trusted was her father, who died shortly before Tekken 2. Ironically, after her father's death, Nina was controlled by Ogre, and was thus unable to feel any emotion. Nina's personality remains monotonous yet sadistic when it comes to teasing Anna. Nina's win poses range from tomboyish and masculine to flirtatious, usually by placing a foot on top of the opponents body or showing off her body figure. Although she is an assassin, most of her missions are inclined for the good of the world, though she was hired to kill Steve by the syndicate during Tekken 4 and also assisted Jin when he started a world war during Tekken 6.

While searching for Jin, Nina and Tekken Force are suddenly confronted by Heihachi, who has returned to reclaim the Zaibatsu. Defeated, Nina is forced to work for him and stands behind him while he announces The King of Iron Fist Tournament 7. Although she questions Heihachi's motives, Nina follows him as he travels to the Archers of Sirius to get them on his side. They infiltrate their main base and take out several exorcists before Heihachi fights and defeats Claudio Serafino.

They then continue their search for Jin, following on the rumors on something evil appearing in the Far East. But Nina later finds that Lars has taken Jin into hiding, saying that things have become more complicated. After the Tekken Force fails to capture Jin, Alisa and Lee, Nina decides to take the SWAT team and go in herself. At Lee's medical facility, Nina launches a surprise attack and confronts Alisa in battle. While staying her ground, the Tekken Force captures Jin and holsters him away. But Lee manages to hijack the helicopter and traps Nina inside the facility.

As the rebels make their escape, Nina is trapped in an explosion set off by Lee. However, she survives the attack, pondering as to why Lars and his group are sheltering Jin. Nina then decides that it will be fun to watch. After failing to apprehend a comatose Jin Kazama from Violet Systems while under her last orders from Heihachi, Nina Williams decided it was time for her and the Mishima Zaibatsu to go their separate ways. On her first private assassination job, she was tasked with infiltrating a mafia wedding... posing as the bride.

As it turns out, the wedding was actually between a G Corporation executive secretly part of the mafia, and the now-retired Anna Williams. [5] Before the wedding ceremony could start, Nina managed to steal Anna's wedding dress from her dressing room, and successfully infiltrated the wedding posing as the bride. Shortly afterwards, a firefight broke out where Nina took out all her targets, including Anna’s fiancé.

However, the commotion had attracted the Tekken Force, who had been dispatched to suppress the violence, and they gave chase. With the Tekken Force, and possibly Anna too, in hot pursuit, Nina made her escape. That's when she bumped into a man she found vaguely familiar. The man wouldn't leave her alone. He seemed to have something he wanted to say to her... Nina decided that a confrontation was her best chance of escape.

Ending Description: After defeating Steve, Nina is soon confronted by the Tekken Force. She throws a knife at one of the soldiers and quickly follows up with a flash grenade. Nina then escapes, leaving her unconscious son behind.