Karella & Karelen were both created by the Mechanics intended to be used as living weapons for the field of battle. Little did they know how effective they may become. Karella was originally intended to be used as a psychic weapon, following on from a dark experiment to create a super psycher, she would become far more than this.
When unleashed on her first ( and as it turned out only ) combat drop, Karella met the battlefield, awash with psychic energy, unable to control her abilities, Karella absorbed all of the psychic turmoil of the battlefield, further more the build up of power couldn't be contained, especially by one who was not used to such overwhelming power. What happened next was mostly down to conjecture. Mostly it was believed that Karella unleashed the massive build up of power, wiping out friend and foe were they stood.
Worse was to come for Karella, upon unleashing the torrent of power, she had unwittingly opened a gate into the warp. A creature of that dimension seeing an opportunity, latched itself partially onto Karella's mind before the gate could be closed. Strong willed though she was, Karella could not stop the creature reimagining her form to better suit itself. However, Karella retained her own part of her mind, this caused her to become alarmingly unpredictable, as she wrestled for control of her body with the creature, thankfully the Wolf came to her aid. Hearing of the near disaster, he knew she would be a great ally. Knowing of her predicament, the Wolf had a null room made for her, where she could remain safe from psychic turmoil, until her special abilities were required again.
Karelen's story was of a similar vein. Karelen was also created as a weapon, although of a different type, given the abilities of a n arcoflagellent, Karelen was intended as a weapon of fear, sent among the enemy to sow discord in the ranks with her fearsome arcoflails.
Again it was on her first outing that trouble would rear it's ugly head. Taken a board a hulk during a cleansing mission, Karelen slipped away from her handlers, making her way deep into the hull of the enormous ship. Feared lost to whatever may lay inside Karelen was abandoned to her fate. Little did any of this concern Karelen, who in her own unknown state of mind wandered the corridors of the ship, her flails sparking off of the floor and walls as she went. As she did so, a voice whispered to her.
Many months later, an explorator team found Karelen alone and muttering to herself, when they attempted to take her with them, she did not resist. It is said that Karelen did not resist because the hulk had told her of her fait and that the Wolf would come as her saviour. It is also rumoured that the hulk whispered many secrets into her mind but for what purpose remains unknown.