Robert and Jane Takahama moved with their daughter to New York City from Ojai, California, for a chance at a better life. Because of her father's work at the United Nations and her mother's psychiatric practice, Hallie grew up in relative luxury and comfort. That all changed on her 15th birthday, when the menace known as Onslaught killed her parents, razed her home and destroyed her neighborhood during his attempt to take over the world.

In the aftermath, the mad geneticist Arnim Zola abducted Hallie, along with a number of other children. She was subjected to experiments that made her feel as if she were being torn apart from the inside. The procedures made her faster and stronger, filling her to bursting with energy. At the first opportunity, Hallie used her new powers to escape. She then sought out the Thunderbolts, who returned with Hallie to rescue the other captives and defeat Zola. Subsequently, Hallie adopted the name Jolt and joined the team.

During this time, the young hero led a double life: At school, she was the surly Hallie Shimosato; once the bell rang, she was Jolt. She and her teammates defeated the Secret Empire and the Imperial Forces, the Crimson Cowl, and Graviton, and hunted down the Hulk. Ironically, she died not in the guise of Jolt, but as her alter ego: Hallie was murdered after school while she and her friends were at a coffeehouse.

Jolt's Thunderbolts' teammate Techno stole her body from the morgue, hoping to isolate the course of her biokinetic powers. His experiments caused a regenerative effect that revitalized Jolt, transforming her into a being seemingly suffused with bioelectric energy.

After being stranded on Counter-Earth with most of the Thunderbolts, she chose to stay behind to help the devastated planet as one of the Young Allies. However, Jolt made a brief return to Earth, in order to help both the T-Bolts & Avengers to stop the out-of-control Moonstone (who've possessed two moonstones at the time and was losing control when she absorbed the Liberator's energies within her).