Jax was a Mirialan of the male gender, and of a young age. He was held captive within the confines of the vault at Tantiss Base, where his designation was SP-32. His imprisonment, alongside two other children named Eva and Sami (a Pantoran), stemmed from their elevated midi-chlorian count. Following an unsuccessful attempt to break free, Jax was subjected to a stun and confined in isolation for a period of two local days. Ultimately, he and the other imprisoned children managed to flee Tantiss with assistance from Doctor Karr and the group known as the Bad Batch.