Initially, Zep was a fairly standard Irken soldier. While she was oddly hesistant in her duties, she was still fairly good at combat nonetheless, and had no real problems until reaching this rank.
Unfortunately, the empire would soon catch onto this tendency, and forced her to volunteer for a new experiment, that being using a type of bacteria thatwould theortically increase agression in Irkens. While covered up as simple tests, this was a scheme to 'cure' nicer irkens and increase agression during warfare. This plan ended up backfiring on multiple levels, as the few Irkens it was used on became more agressive towards everyone, including other Irkens. While the ability to feel any kind of remorse or .sympathy was disabled as planned, this, combined with the former, lead to many casualities among Irkens.
Due to being subjected a particularly large amount of the substance, these symptoms were particularly bad with Zep, who became almost incapable of feeling (both emotional and physical.) All of the test subjects were deemed "useless and dangerous" and disposed of immediatly, Zep's survival being mostly luck.
Zep is, in general, very bitter and cold, as well as slightly selfish regarding her goals. Outside of that, she tends to show very little emotion, or any kind of desire outside of revenge. While she can show empathy on occasion, it is usually to victims of similar predicaments to her's, and it usually doesn't change her actions towards them.
She was supposedly very kind before her infection and mental trauma, though not enough to seriously abstain from Irken violence.