Although she was not completely evil, the reason of why she was antagonistic at the start because of her dislike for the Matoran and their kind, whom she called "top-dwellers" and her assault on the Toa Metru during the repair in the Archives. However, she eventually became an ally of the protagonists as the story progressed.
Not much was known of Krahka's past but it was once revealed that she came from the species who was the victims of the Visorak as the spiders hunted every one of them during the attack in her island. Krahka then fled to the island of Metru Nui where she hid in the underground tunnels which were located below the Archives in Onu-Metru. Believing herself to be the last of her kind, she begins to develop a intense dislike for the Matoran and their kind, whom she referred as "top-dwellers".
City of Legends
About 1,001 years ago during the events of the storyline, the Toa-Metru were on their way to the Coliseum after the search for the six Great Disks and their battle against the Morbuzakh as they presented them to Turaga Dume, who turned out to be Makuta Teridax in disguise. In their way to their destination, the Toa then approached by the Matoran who told them of the two problems: the leakage that threatened to flood the Archives and the another is the Onu-Matoran known as Mavrah who was hiding in the underground cave along with several Rahi. The Toa Metru then decided to split up as Vakama, Nokama and Matau went to the Archives to fix the leakage. After the three Toa entered into the Archives, Krahka, having sensed their presence quietly stalked them, watching them fight and learning their language. Krahka's first contact was with Nokama. Taking the form of a wild Rahkshi the Toa had battled earlier, she battled with Nokama and knocked her unconscious as Krahka took her to her lair and tied her in the web. Krahka then assumed the form of Nokama and she proceeded to approach towards Vakama. At first, she was unable to speak Matoran, and could only mimic the words spoken to her, converting them into frangmented and short words. After ths short conversation, Krahka then battled Vakama and attacked him with jets of water, knocking him unconcious.
Having defeated Vakama, Krahka then assumed his form and confronted Matau. However instead of another attack, she uses her better developed speaking skills
Krahka have the a very distinct personality, considering that she was a Rahi. She is very defensive.