Xenon has a vendetta against all Supergirls from all worlds because one imprisoned him at the dawn of time. He goes to the post-crisis era where he captures Kara. Back in the Pre-Crisis era, Linda was confronted by The Spectre saying that it was not going to work with Linda dying instead of Kara.Linda agreed to return to her time and send Kara back as long as The Spectre ensured that her daughter survives. The Specter agrees and Linda is transported to Xenon’s palace. Linda confronts Xenon, defeats him, and rescues Kara.
Xenon has hunted for all females who bare the crest of super girl on their breast for thousands of years since being trapped. With the aid of his servant Fatalist, he roundup supergirls from multiple Worlds, Realms, universe's & time's. Dragging them back to his prison at the dawn of time, where all life starts and ends. He keeps them there to slowly kill them & watch them suffer. This slowly makes the seal to his prison crumble. Hoping to free himself again so he can end all Supergirls throughout time & space forever.