Hallie Takahama had just turned fifteen when New York was attacked by the psionic Onslaught and his robot Sentinel army. Hallie's parents were slain, and she became the protector of several younger children during the crisis. She and her charges were abducted for experimentation by the geneticist Arnim Zola. Mutated into superhuman form, Hallie escaped and sought aid from the Thunderbolts, not realizing they were secretly Baron Zemo and the Masters of Evil. As part of their heroic pose, the Thunderbolts captured Zola, and when Hallie's involvement was telecast, Zemo, as Citizen V, agreed to let her join.
The enthusiastic Jolt served with the Thunderbolts for weeks before Zemo, as part of his larger scheme, revealed the team's true identities; as the team fled, Jolt stowed away on their craft, and when some of the Thunderbolts questioned their involvement, she persuaded them to become genuine heroes and help defeat Zemo. Still on the run for past crimes, the Thunderbolts fell under the leadership of the Avenger Hawkeye, who wished to help them redeem themselves to the public. To Jolt's annoyance, Hawkeye insisted that she complete high school, where she was targeted by Scourge, an assassin controlled by government operative Henry Gyrich. Scourge apparently killed Jolt, who was mourned by her teammates. However, Jolt's superhuman form retained some semblance of life, and her former teammate Techno absconded with her body, holding her in stasis for weeks as he considered her condition, ultimately releasing her when Scourge attacked the Thunderbolts' base. Now partially paralyzed but able to assume an energized form, Jolt joined her teammates in defeating Scourge and exposing Gyrich's activities. Now a ward of the state, she joined the government super-team the Redeemers.
After joining the Redeemers, Jolt was unable to return to school due to having such a public civilian death and burial. Instead she was schooled by S.H.I.E.L.D. and went through a strenuous daily therapy regimen to learn to walk normally again. Tragically, most of the Redeemers perished fighting the godlike Graviton and Hallie's best friend Charlie (Charcoal) was presumed destroyed. Jolt survived, and she and the Thunderbolts were transported to Counter-Earth, a duplicate Earth on the other side of the sun. The team labored to help the problem-ridden world recover, and when the Thunderbolts returned to their own Earth, Jolt chose to remain behind and continue the rebuilding process alongside the teen team of the Young Allies. Jolt briefly returned to aid the Thunderbolts during a crisis with the Avengers but is again on Counter-Earth.