During the Ikaruga Civil War, Karenjina and her younger brothers fell on hard times. Since she was desperate for money, she willingly sold herself to a laboratory that studied souls, and it was here that she was forced to awaken her Drive - Seagull. Eventually, she was rescued from the facility by Captain Grimwood Huster of the NOL, but when she went back to her home, the 5th Hierarchical City of Ibukido, it had already been completely annihilated by the Nox Nyctores - Gigant: Take-Mikazuchi; her brothers presumably killed in the blast. Karenjina joined the NOL in a search for vengeance and to end the war that took her brother's lives. She was placed under Grimwood's command in his squadron.
Ikaruga Civil War
Near the end of the war, Jin Kisaragi was assigned to the Ninth Squadron, and Karenjina took an immediate dislike towards him, remarking that he wasn't needed. Shortly after their unpleasant meeting, the squadron was deployed on an emergency mission to recover a Nox Nyctores that was stolen by Sector Seven, but they had arrived at the destination too late, and were ambushed by the corpses in the lab. Thanks to Karenjina's Drive, they located the “Necromancer” and disposed of it. Unknown to the Ninth Squadron, Relius Clover was watching nearby, and took note of Jin's weapon (the Mucro Algesco: Yukianesa) and Karenjina's Drive.
An order later came through to attack the Wadatsumi Castle, but Grimwood took the squadron on a diverting path to find a weapon capable of halting the flow of seithr so it could be destroyed, and potentially end the war. Karenjina's Drive allowed them to find a suspicious entrance, but she was left behind on Grimwood's orders with Corporal Honoka (in reality, Hazama).
Before long, Karenjina was captured by the NOL's Zeroth Squadron, led by Meifang Lapislazuli, and was interrogated because of Grimwood's ties to Kokonoe. The torture inflicted on her left her in such a state that she was now permanently incapable of activating her Drive. The death of Grimwood would deeply affect her, and Jin later visited her in hospital.
It's unknown what happened to Karenjina after the Ikaruga Civil War, and if she stayed with the NOL after her torture and Grimwood's murder. In its aftermath, Jin hunted down Meifang under the orders of Kagura Mutsuki. Alongside Mai Natsume, he defeated her, finally avenging the Ninth Squadron. 
- BlazBlue: Variable Heart, Chapter 18