Bilsa was an Orokin of the Sectarus class. Nothing is known about her before the Empire's fall.
After The Collapse
At some point after the betrayal of the Tenno, Bilsa and Executor Avantus had to flee from an Orokin Tower being overrun by Infested. The first time she is seen is when she and Avantus are abandoning a group of other (presumably Orokin) survivors within the tower to save themselves. Bilsa made comment on Avantus' decision to leave behind of other survivors, but altogether didn't seem appalled by the action, as they make their way for a hangar to escape the overrun tower.
Shortly after, they encounter a group of Grineer. At first Bilsa is excited to see them, thinking them soldiers, but when Avantus points out they are merely workers she demands they kneel before Avantus. When they find their path is blocked by Infested, Bilsa wonders aloud if they couldn't make it through on their own, but Avantus reminds her they only have pistols and no Corrupted to back them up. Bilsa then suggests the Grineer help them, but Avantus again reminds her they have no weapons - at which point the biggest Grineer Veytok in the group heads to a tool case (which Avantus opens for them) and took up cutting tools and safety equipment as weapons and armor.
Before Grineer start fighting through the Infested for them, Avantus reminds Bilsa that they wont be taking the Grineer with them. Bilsa is shocked that she would say such a thing while the Grineer could hear her, but Avantus reminds her that the Grineer simply are unable to comprehend much of what they're saying. The Grineer fight through the Infestation while the two of them stayed safely in the back, allowing them to reach the hanger. Avantus orders Bilsa to open the shuttle door.
As more Infested begin charging down the path that they came through Avantus orders the Grineer to go hold them up, but they refuse to listen. When Bilsa announces that she has the shuttle open Veytok murders Avantus with a saw through the spine, before telling Bilsa she now works for them and to make the ship go.
Some unknown time after this, Bilsa was able to get in contact with a man named Alarez, informing him of her situation and that she doesn't even feel Orokin anymore. After she tells him she is a Sectarus, and being surprised to realize that he wasn't, she attempts to caution him against coming, telling him that the Grineer in command (who now calls himself Veytok) is too dangerous, that she's been helping him amass an army of Grineer.
Alarez refuses to listen, telling her that the System is in chaos with the Executors and Council being either dead or missing; Bilsa is confused as to how he's managing to pilot the Executorial Frigate without an Executor. Together they formulate a plan to trap the Grineer in the docking bay airlock while Alarez and a team board through an emergency hatch. She goes to meet them, only to be waylaid by Alarez's guardsman and a Dax. Alarez uses a genetic descrambler, to Bilsa's surprise, to scan her for a sample of her genetic code so he can have full access to the Executorial.
Alarez informs her that he has to kill her to keep her from outranking him and orders Bilsa to cut off life support to the Grineer in the airlock. Bilsa admits that she can't, informing him that the Grineer are already overrunning his ship. Before Alarez can process, Veytok drops down on the Dax, killing him instantly, and is followed by others who kill all of Alarez's guardsman, leaving only him alive.
Bilsa admits that she is now working with the Grineer, and asks him if he'll keep her company, as the Grineer aren't much for conversation. Before she can even finish some of her questions, Veytok kills Alarez, enraging Bilsa, but he reminds her that they had what they were after - the ship and the lab on board - and that she doesn't need visits from others, she's Grineer now.
- As there have been no female Grineer expressly mentioned in the Orokin Era up to this point (even though Bilsa was more technical Grineer than genetic one) it is possible that they didn't exist, and that Bilsa is the source for all female Grineer seen in-game, or at least the original.