Alli was born to Charlie and Renée Swan just slightly after her twin sister Bella. Following their parents' divorce, Bella and Alli moved to Phoenix, Arizona with their mother. They started attending the twins-only high school Apollo High at fifteen, where they befriend the Sanders twins Savannah and Adana. On her sixteenth birthday, Alli gets her bonus (enthusing that it allows her to get "twice as much done") and spends the next week experimenting on her powers with Bella. After being evaluated, she joins the Gemini Guard as Bella's optional/emergency support, junior grade, stratum 4.