I was thinking of another theory.
Do any of you would wonder if Mio and Wataru find out each other as the pearlshell fangire and kiva? If they learned of each other and understand the goings on, Saga/Taiga would try to kill his half-brother, but Mio would sacrifice herself to save him. Wataru was shocked of her killed by Saga and she falls to Wataru's arms. Wataru would want to try to save her, but she would said her last dying words about a true threat (and not Saga). She would also say that she loves him no matter what in spirit. Mio then dies and Wataru goes berserk and fights Saga to avenge her. (think of this fight like in DMC3 of Dante and Vergil) Wataru goes crazy after being impaled by Saga's jacoder and unleashes to the true fangire in him and destroys the city and tries to kill Shima. But Megumi and Nago try to calm him down and Wataru reverts himself back from flight mode to human form and falls to Megumi's arms crying.
