Jenni comes from a long line of speedsters but didn't appear to have inherited their powers. Her grandfather was Barry Allen, The Flash. Her mom and uncle briefly used their speed powers as the Tornado Twins until they were murdered by a of alien Dominators. Fearing for his daughter's life, Jenni's dad moved them to Aarok. A few years later, the Dominators found and abducted them so they could examine Jenni's genetic makeup. Under the strees of the situation, Jenni's speed powers finally manifested, and she escaped with her father. Jenni took refuge with U.P. geneticists eager to study her power. Later, she was drafted into the Legion. XS is one of the most vivacious Legionnaires. She tends to develop crushes, and her open personality makes it difficult to conceal these sometimes embarrassing feelings. XS briefly traveled back to the 20th century to meet her cousin Bart (Impulse) and the rest of the "Flash Family". They gave her the confidence to explore and develop her powers further.