What happened in previous books...
Kai has kept it a secret from his team that what the Abbey had really been training him into wasn't just to become a beyblading pawn to his grandfather, but as a ninja-like, beyblade armed assassin. Kai has killed before, but intends to keep his skill and past buried and forgotten-until an unknown beyblader and a mysterious girl sing out, not only Tyson and Max's bitbeasts, but their souls as well. The singing girl, named Ayah, turns out to be just as much a prisoner as Tyson and Max's souls and nearly dies when she tries to avoid stealing Ray's soul as well. Not knowing she has survived, her captors leave Ayah alone long enough to give Kai a map to Tyson and Max's souls, to which he uses his bad-a beyblade assassin's skills to break in, slice the Achilles tendons of guards, avoid armed men, and escape with the souls and bitbeasts of his team mates.
In the second book, Kai has hopes that his incursion has been unnoticed, but he is soon distracted by his teammates adoption of the abandoned, injured Ayah, who is as beautiful as she is mysterious. Kai is not so quick to forget her inhuman abilities to control sound and sing out human souls. It doesn't help that he finds he isn't as immune as he'd like to be to her beauty and kindness, which he attributes to her inhuman qualities. When Tyson throws a homemade tournament for his birthday, Kai pays little attention to it, until Ayah leads him to a dark flight of stairs where another assassin, trained in the Abbey just as Kai was, is closing in for their kill. At the last minute Kai smashes their sharp assassin beyblades with Dranzer, but in the fight something strange happens and Kai is overwhelmed by Dranzer's explosion of flame. Ayah insists she just heard something with her strange, ultra sharp hearing, but as the flames die down and Kai finds himself once more in her arms, he finds himself trusting her less than ever. Nothing will harm his teammates, even if they happen to be gorgeous, gentle, and soft.
Come the opening of the third book, Kai is in the hospital suffering from severe burns. He demands to know what his ex-fellow Abbey assassins had to do with Ayah, and she doesn't know, but she is determined to stop them from harming the BladeBreakers. She offers to heal Kai, and in the process, lures him into a three day slumber. When he wakes up, not only is Ayah gone, his burns have completely healed, the president of the United States has been assassinated, and another assassin is waiting for him.
Kai is kidnapped and taken to a secret, underground bunker held by none other than a winged man who claims to be of the same species as Ayah, and who intends to use the abandoned Abbey assassins to clear the world of humankind so his own can flourish. Ayah is to be his Eve. But Kai, not keen on being anyone's captive, smashes his way to Ayah with the help of the also captive Tala. What Ayah and this...black angel are is made clear and Kai must defeat Cain, who so easily cowed the once fearless Abbey assassin's with his ability to kill if anyone on Earth is to survive. With the help of the Bladebreakers (who appear out of the blue because they're obsessive-compulsive friends like that and aren't likely to leave one of their own in trouble), along with the boosting ability of Ayah's voice, Kai burns Cain to death, but at the cost of burning himself as well.
In the fourth book, Kai comes to in the opposite state he blacked out in-freezing to death, and on a boat heading back for the mainland. Before his companions can celebrate, Max suddenly dives overboard and vanishes into the ocean. The others rush to the hospital, and Kai, always the lone wolf and only wanting to be warm, dodges going and head back to the dojo, where he, in a fit of desperation on finding water makes it worse, starts a fire and dives into it. He wakes up a scarlet, winged denizen of fire, to the surprise and delight of Tyson and Ray, who thought him and Max dead. Ayah also goes through drastic transformations. Since Kai can't find Dranzer, he figures they have become one, and tries to dissuade an excited Tyson that turning into a flying, inhuman freak isn't as cool as it sounds. Kai, and possibly the still missing Max, will never lead normal lives. Cain and the assassination of Ayah's family are already testaments that there is no room in the world for the kind of beings they have become.
Of course Kai has no time or patience to deal with his newly discovered feelings for Ayah. He already knows a man raised from a boy for cruelty and killing could never have the tenderness to make a woman happy, let alone a family. So what more is there to say?
In the fifth book, Kai has spent the last month furiously trying to regain his lost physic and strength that his unplanned transformation took from him. On returning to Tyson's, he is faced with the reality of his love for Ayah, as well as his anxieties concerning his own future and that of his teams. Just as a fully alive and also transformed Max works with the others to go to LA so his mother can research them, Tala calls with a warning of nuclear catastrophe. The world treaty ceasing the production or existence of firearms has been shattered by the American president being assassinated and the discovery of Biovolt's Abbey and their trained assassins. They must get out. But no sooner have Kai, Tyson, and Ayah found a boat to escape on to America, they are captured by a group that know far too well what they are, and how to keep them contained. Facing dismemberment in the face of science or whatever these hunters want from them, it seems to be the end of the line. A harsh reality that they are no longer seen as human faces them.
But then Tyson, still human, and therefore underestimated, manages to wriggle them loose. But they're in the middle of the ocean, on a ship full of their captors with no qualms about killing one or two of them. With bullets and darts flying, Tyson takes a stand with Dragoon, and Kai takes the fall for the bullets heading his way.
The last thing Kai perceives is the bright blue light of Dragoon and Ayah pulling out too many poisoned darts from his ribs and chest. Then all goes black, with little hope for waking up.
Now on to the sixth installment of Before Beasts...