That's another personality in her that the Phantom had mentioned earlier - sort of like the awakening of Saya. She went into this berserk mode once when she and the group went to the old mansion in Vietnam - even Haji couldnt stop her, but her brother managed to

2 eps in the zoo and bravo, we get to know more about the past. Eventually Saya met her sister, Diva - although they both are the same species but looks like Diva is much more stronger than Saya. In other words, Saya is no match at all for Diva. Even Haji got outsmarted by Diva's Chevalier, Solomon. 3 good eps here, pity Riku has to become Saya's Chevalier in the future