My current theory is that the Athetos Trace fights at the end is an older clone-- "Plan A." The original Athetos arrived and perhaps was even the cause of the great wars of Sudra that trapped the Rusalki on the surface. He long ago left through the Breach somehow. The Rusalki used a rebirth chamber to revive him and hope the new clone would let them off the planet, but he rebelled and decided to destroy the Rusalki. (Drushka and/or Katrahaska, who may be one and the same, aided him in this quest.) The Trace we play as is Plan B.