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- “I'm not a killer. I'm a healer. I fix things. That's what I do.”
Nina was the daughter of two Watchers, Merrick and Helen Jamison-Smythe, and had a twin sister, Artemis. When she was eight, her father having passed away, Nina, Artemis, and their mother moved from California to Arizona, where they survived a house fire. With magic protection, Helen was able to rescue one of the twins at a time, and being chosen as last left Nina asthmatic, her lungs severely damaged in the long lasting exposure to the fire.
Since then, the twins grew up in the grounds of the Watchers Academy, and would rarely see their mother anymore. In her studies, Nina wasn't allowed to perform the same training as those who wanted to become full Watchers did, including Artemis, so she trained to be a medic for the Watchers Council.
Nina believed to be overprotected due to her mother considering her incapable and even invaluable, the same reason she had thought to be saved last. Nina would learn years later, though, that Helen wanted to prevent the moment that triggered Nina to become a Slayer, her status as a Potential Slayer the reason as well her mother knew she would survive the house fire.
In 2002, the Council suffered multiple attacks from acolytes of the First Evil in attempt to terminate the Slayer line. Nina and her family were among the few members of Watchers society that survived, and would stay in a hidden castle in Shancoom, Ireland.
Nina and her sister spent eight years in Ireland before the destruction of the Seed of Wonder, in 2006. Considered the last Slayer to be called before the end of magic, Nina was activated in the same day, but only noticed it two months later, after killing a hellhound with her bare hands. Since then, she would often encounter Buffy Summers in their dreams, and express the grudge she hold against the Slayer for her father's death.
With the discovery of her powers, Nina was trained by Leo Silvera, the young Watcher she had a crush on three years earlier. Facing hellhound attacks on the Academy and the appearance of the hunted demon Doug, they acted with her friends Artemis, Rhys, and Cillian in both Shancoom and Dublin. Nina's first major fight was in a demon fight club in O'Hannigan Ironworks, where she rescued the Slayer Cosmina Enescu after having dreams of her as a prisoner.
Investigating such events, Nina eventually discovered an enemy acting within the Council, the Watcher turned succubus Eve Silvera, who had already killed her great-uncle Bradford and Cosmina. To protect her sister from the demon, Nina sacrificed her own Slayer powers, letting Eve absorve them instead. Still, after understanding Buffy's own struggles and choices, and her own identity as a Slayer, Nina was able to defeat Eve, close a newly open Hellmouth, and save the world — although, not without also leaving behind Leo, with whom she was just recently romantically involved.
After this, Nina and her fellow colleagues decided to open the doors of the Academy to rescued demons from Naked Grains, as well as the recently called Slayers they intended to seek.