Xneen was the wife of Mar Novu.
Xneen was born on the planet Maltus, eventually meeting Mar Novu and falling in love with him. Later on, Xneen married him and worked alongside him in order to peer into the beginning of the creation of their universe.
Transporting Mar to the dawn of time
Xneen and Mar were scientists that created a time machine in order to peer into the beginning of the creation of their universe. During this time, Xneen designed a suit for Mar to use in their experiments. She monitored their experiments as Novu worked to enter the temporal zone. However, one of their experiments was interrupted thanks to Lex Luthor, who had arrived from the Vanishing Point and had subsequently knocked Xneen unconscious. Luckily, Supergirl and Ryan Choi prevented Lex from manipulating the timeline to his own ends, despite being unable to stop Novu and Xneen from discovering Mobius and the antimatter universe.
Xneen died at some point after Mar Novu returned from the Netherverse, killed presumably by Mobius.
In the original timeline, Xneen and Mar succeeded in traveling to the beginning of the universe, with Xneen losing contact with Novu, who had found himself facing his antimatter doppelgänger, Mobius.
Xneen death was hard on Mar Novu, her husband, and they loved each other very much. While talking to Lois Lane aboard the Waverider. Mar Novu mentioned he had lost his family and world saying Xneen meant everything to him and was full of life, regretting caring more to his work then her.
Xneen loved Mar Novu very much, caring deeply for him and his safety. According to Novu, Xneen was full of life.