Supposedly dead for years after an explosion caused by a dying Trumain with a grenade while Kagan was looking for something called the Vespers Shards, Rayne spent 60 to 70 years later killing off her half-siblings since she didn't get a chance to kill him herself. After she learns her half-siblings were building tower to release a cloud of chemicals with blood into the air called the shroud, which would allow vampires to roam the city, Rayne destroys one of the towers and learns that Kagan was alive with the Vesper Shard seared into his flesh, which he admitted causes him intense pain but grants him great power. Despite that there were other towers and they had released the shroud and many citizens were killed by not only vampires, but demonic entities as well, Rayne is happy to know that Kagan is alive so she can kill him herself to avenge her mother and her mother's family. She makes her way to a large building, killing several more of her half-siblings and eventually reaches the top.
She finds Kagan and finally gets the fight she wanted since her childhood. Despite being a powerful fighter, Kagan is no match for his daughter and is decapitated. Since Rayne is now the only one with the Kagan bloodline, she takes over his empire. Severus warns her though that now that she's in charge, other vampire overlords, as powerful or maybe even stronger than Kagan would try to come after her to take over his empire.
Kagan was pure evil, and saw his children as mere servants, even leaving one to die after failing to kill Rayne. His towers resulted in the deaths of thousands of innocent people, and even before that, he has raped many women to bear dhampir children and wiped out entire families. He has control of a large vampire empire and even has control over demons.