Eureka is a pale young girl with turquoise hair and lavender eyes and is a pilot of the Nirvash typeZERO. She treats Nirvash not like a mere machine, but as a living being, with consciousness and feelings. However, she can seem distant and awkward to other people - she has trouble communicating with other humans and understanding their feelings. She tends to appear randomly next to people, startling them at times. Initially in the anime, she suffers from frequent headaches, seemingly due to the presence of Renton Thurston. She is the adoptive mother of Maurice, Maeter, and Linck, but is often unsure of her role as a mother, and often asks Renton how she should scold them, and if she is a good mother.
It is later revealed that she is actually a Coralian in human form, sent by the sentient Scub Coral to understand and communicate with humans.
After she is revealed as a Coralian, Renton does not reject her as she feared but rather accepts her for who she is, not what she is, which results in a further expansion of her understanding of human emotions.
Her name is usually not pronounced like the word "eureka" in English (pronounced as eau-wreck-uh instead of you-ree-ka). During the previews at the end of each episode, Eureka is referred to as "the girl".